REESE  LIBRARY 


UNIVERSITY  OP  "CALIFORNIA. 


t/lcce&.sjp n  No .        '  &  O.  cj  O  * .    CL /  s s  ? 


WORKS  OF   WILLIAM  KENT 


PUBLISHED    BY 


JOHN   WILEY   &   SONS. 


The  Mechanical  Engineers'  Pocket-Book. 

A  Reference  Book  of  Rules,  Tables,  Data,  and 
Formulae,  for  the  Use  of  Engineers,  Mechanics, 
and  Students,  xxxii  +  noo  pages,  i6mo,  morocco, 

$5.00. 

Steatn-Boiler  Economy. 

A  Treatise  on  the  Theory  and  Practice  of  Fuel 
Economy  in  the  Operation  of  Steam-Boilers. 
xiv  +  458  Pa£es>  T36  figures,  8vo,  cloth,  $4.00. 


STEAM-BOILER  ECONOMY. 


A   TREATISE  ON  THE  THEORY  AND 

PRACTICE  OF  FUEL  ECONOMY 

IN  THE  OPERATION  OF 

STEAM-BOILERS. 


BY 

WILLIAM   KENT,   A.M.,  M.E., 

Consulting  Engineer;  Associate  Editor  of  "  Engineering  News  "; 

Author  of  "  The  Mechanical  Engineer's  Pocket  Book"; 

Member  American  Society  of  Mechanical  Engineers,  American 

Institute  of  Mining  Engineers,  American  Society 

of  Heating  and  Ventilating  Engineers. 


FIRST  EDITION. 
FIRST  THOUSAND. 


NEW   YORK: 

JOHN  WILEY  &  SONS. 

LONDON  :  CHAPMAN  &  HALL,  LIMITED. 

1901. 


3 


Copyright,  1901, 

BY 

WILLIAM  KENT. 


ROBERT  DRUMMOND,    PRTHTER.    KF.W   VORTf. 


PREFACE. 


IN-  the  year  1875  the  author  made  his  first  evaporative  test  of  a 
steam-boiler.  It  was  the  Pierce  rotating  boiler,  which  was  tested  at 
the  Centennial  Exhibition  the  following  year.  It  had  certain 
peculiarities  of  design  which  were  supposed  by  the  inventor  to  make 
it  more  efficient  than  any  other  boiler  then  on  the  market.  The  test- 
ing of  this  boiler  and  of  two  others  during  the  same  year  led  the  author 
to  study  seriously  the  problem :  "  On  Avhat  conditions  does  the  fuel 
economy  of  a  steam-boiler  depend?"  For  three  years,  1882-5,  he 
was  in  the  employ  of  the  Babcock  &  "Wilcox  Co.,  and  it  was  part  of 
his  work  to  make  evaporative  tests  of  the  boilers  made  by  that  com- 
pany, and  of  other  kinds  of  boilers  for  comparison,  in  different  sections 
of  the  country,  and  with  all  kinds  of  coal.  In  connection  with  his 
office  practice  from  1890  to  the  present  time,  he  has  had  occasion  to 
make  nearly  a  hundred  boiler-tests,  with  different  boilers,  fuels,  and 
furnaces.  Besides  having  this  practical  experience,  together  with  the 
habit  of  studying  critically  the  result  of  each  test  for  the  purpose  of 
drawing  conclusions  from  it,  the  author  has  been  a  constant  student 
of  the  literature  of  the  subjects  of  boiler-testing  and  fuel  economy, 
which  from  time  to  time  appears  in  the  transactions  of  engineering 
societies,  in  the  technical  press,  in  trade  catalogues,  and  in  books. 
He  has  thus  been  enabled  to  compare  theory  with  practice. 

Many  books  have  been  written  011  the  subjects  of  boilers,  furnaces, 
and  fuels,  but  in  none  of  them  does  it  seem  that  the  problem  of  steam- 
boiler  economy  has  been  treated  with  the  thoroughness  which  its  im- 
portance deserves.  Most  of  the  treatises  on  boilers  devote  the  greater 
part  of  their  space  to  details  of  construction,  and  only  a  small  space 
to  the  subject  of  fuel  economy.  There  appears  to  be  a  demand  for 
a  new  book  which  shall  treat  solely  of  steam-boiler  economy  and  of 
subjects  related  thereto.  To  supply  such  a  demand  this  book  is 
offered. 

iii 

92386 


iv  PREFACE. 

A  few  words  as  to  the  plan  and  scope  of  the  book.  The  first 
chapter  contains  a  statement  of  principles  and  definitions  and  a  very 
brief  survey  of  the  whole  ground  intended  to  be  covered  in  the  re- 
mainder of  the  book.  Chapter  II  treats  of  the  chemistry  of  fuel  and 
of  combustion,  of  the  heat  generated  by  combustion,  and  of  the  tem- 
peratures produced  under  different  conditions.  The  discussion  of  the 
subject  of  temperature  is  believed  to  be  more  complete  than  that  given 
in  any  other  work.  Chapter  III  is  a  brief  one  on  coal  and  its  heating 
value,  including  a  table  of  analyses  and  heating  values  of  American 
coals.  Chapter  IV  is  much  longer,  and  is  a  condensed  treatise  on  the 
coal-fields  of  the  United  States,  giving  their  location,  with  the  analyses 
of  the  coals  mined  in  each  State  or  district.  The  space  given  to  this 
subject  is  believed  to  be  justified  by  the  close  relation  which  exists 
Between  the  economy  of  a  boiler  and  the  quality  of  coal  used  in  it. 
Chapter  V  is  a  discussion  of  tests  of  the  heating  values  of  American 
and  foreign  coals,  and  shows  the  relation  of  the  heating  value  to  both 
the  proximate  and  the  ultimate  analysis.  It  reviews  the  work  of 
Johnson  and  of  Lord  &  Haas  on  American  coals,  and  of  Scheurer- 
Kestiier,  Mahler,  and  Bunte,  on  foreign  coals.  Chapter  VI  treats  of 
fuels  other  than  coal,  including  peat,  oil,  gas,  bagasse,  etc.  Chapter 
YII  treats  of  furnaces,  methods  of  firing,  smoke-prevention,  mechanical 
stokers,  and  forced  draft. 

In  Chapter  VIII  the  discussion  of  the  boiler  itself,  and  of  the 
efficiency  of  its  heating  surface,  begins.  The  plain  cylinder  boiler  is 
taken  as  the  simplest  form,  and  in  an  elementary  manner  it  is  shown 
how  the  fuel  economy  depends  on  the  rate  of  driving  as  well  as  on 
other  conditions.  In  Chapter  IX  the  same  subject  is  considered 
further  by  the  mathematical  method.  There  is  here  published  for 
the  first  time  a  formula  for  efficiency  of  heating  surface  which  con- 
tains all  the  variables  affecting  the  problem  that  are  measurable. 
They  are :  heating  value  of  the  fuel,  temperature  of  the  water  in  the 
boiler,  radiation,  weight  of  chimney-gas  per  pound  of  combustible, 
and  rate  of  driving.  It  contains  only  one  coefficient  of  performance, 
"  a,"  which  is  not  measurable  as  a  concrete  quantity,  but  is  a  figure 
that  may  be  derived  from  the  results  of  boiler-tests,  and  is  useful  in 
comparing  one  test  with  another.  Much  of  this  chapter  will  be 
skipped  by  those  who  are  not  accustomed  to  the  use  of  algebraic 
formulae,  but  the  conclusions  which  follow  the  mathematical  treatment 
are  of  great  importance,  and  should  not  be  neglected. 

Chapter  *X  illustrates  and  briefly  describes  the  various  types  of 


PREFACE.  y 

steam-boilers  now  on  the  market,  and  shows  the  evolution  of  many  of 
them  from  earlier  forms.  Chapter  XI  discusses  boiler  horse-power, 
proportions  of  grate  and  heating  surface,  and  boiler  performance. 
Chapter  XII  treats  of  the  "  points  "  of  a  good  boiler,  and  will  be  found 
useful  to  those  who  are  contemplating  the  purchase  of  a  steam-boiler. 
Chapter  XIII  discusses  "  boiler-troubles  and  boiler-users'  complaints," 
and  contains  much  information  that  should  be  serviceable  to  boiler- 
users.  Chapter  XIV  treats  of  boiler-testing,  and  includes  the  "  Code 
of  1899 "  adopted  by  the  boiler-test  committee  of  the  American 
Society  of  Mechanical  Engineers,  of  which  committee  the  author 
was  a  member.  Chapter  XY  gives  the  results  of  several  boiler-tests, 
together  with  conclusions  drawn  from  them.  Chapter  XVI  gives 
tables  of  properties  of  water  and  of  steam,  factors  of  evaporation,  and 
a  brief  discussion  of  chimneys,  with  the  author's  table  of  chimney 
proportions.  Chapter  XVII  is  a  miscellaneous  assortment  of  subjects 
relating  to  boiler  economy  which  were  not  included  in  previous 
chapters. 


CONTENTS. 


CHAPTER   I. 

PRINCIPLES    AND   DEFINITIONS. 

PAGE 

List  of  Subjects  to  be  studied 1 

Heat 2 

Temperature 2 

Heat-unit , pk 

Unit  of  Evaporation 4 

Latent  Heat 4 

Specific  Heat.- 5 

Quantity  of  Heat 6 

Heat  of  Combustion 7 

How  Smoke  may  be  burned 8 

Flame 9 

Transfer  of  Heat , 10 

Capacity  of  a  Boiler 10 

Boiler  Horse-power 11 

Efficiency  of  a  Boiler. 11 

Operation  of  a  Boiler 12 

Efficiency  of  the  Heating  Surface 14 

CHAPTER   II. 

FUEL   AND   COMBUSTION. 

Chemistry  of  Fuel  and  Combustion 16 

Carbon 16 

Hydrogen 16 

Oxygen 17 

Nitrogen 17 

Sulphur 17 

Properties  of  Air 18 

Relative  Humidity 18 

Weights  of  Air,  Vapor  of  "Water,  etc 1& 

Heat  absorbed  by  Decomposition 21 

vii 


Till  CONTENTS. 

PAGB 

Heating  Value  of  Compound  or  Mixed  Fuels 21 

Available  Heating  Value  of  Hydrogen 22 

Available  Heating  Value  of  a  Fuel  containing  Hydrogen 23 

Temperature  of  tlie  Fire 25 

Maximum  Temperature  due  to  burning  Carbon 26 

"                     "             "     "        "         Hydrogen 27 

Temperature  of  the  Fire,  Fuel  containing  Hydrogen  and  Water 28 

Excessive  Carbon  Monoxide  due  to  Heavy  Firing 31 

Calculation  of  Weight  of  Air  Supplied 32 

Heating  Value  of  Sulphur  in  Coal 35 

Hygrometric  Properties  of  Coal , 36 

CHAPTER   III. 

COAL. 

Coal  and  Social  Progress 38 

Production  of  Coal  in  the  United  States 39 

Formation  of  Coal 39 

Progressive  Change  from  Wood  to  Graphite 41 

Classification  of  Coal 42 

Caking  and  Non-caking  Coals ; .  43 

Long-flaming  and  Short-flaming  Coals 43 

Canncl  Coals 43 

Lignite  or  Brown  Coal 43 

Proximate  Analyses  and  Heating  Value  of  Coals 46 

Approximate  Heating  Values  of  Coals 49 

Relation  of  Quality  of  Coal  to  Capacity  and  Economy  of  a  Boiler 50 

Valuing  Coals  by  Test  and  by  Analysis ,  51 

CHAPTER   IV. 

COAL-FIELDS   OF   THE   UNITED   STATES. 

Maps  of  Coal-fields  of  the  United  States Facing  52 

Graphitic  Coal  in  Rhode  Island  and  Massachusetts 52 

Anthracite  Coal-beds  of  Pennsylvania 53 

Semi-anthracite  in  Sullivan  Co.,  Pa 54 

Progression  from  Bituminous  to  Anthracite 54 

Early  Use  of  Pennsylvania  Anthracite 54 

Virginia  Anthracite 55 

Anthracite  in  Colorado 55 

A  nthracite  in  New  Mexico 56 

Bituminous  and  Semi-bituminous  Coal-fields 56 

Appalachian  Field  in  Pennsylvania 57 

Analyses  of  Pennsylvania  Bituminous  and  Semi-bituminous  Coals 59 

Maryland  Semi-bituminous  Coal 63 

Virginia 63 

North  Carolina. .                                                                64 


CONTENTS.  IX 

PAGB 

West  Virginia , 64 

Eastern  Kentucky 65 

Tennessee 66 

Georgia,  Alabama,  Ohio '. 67 

Northern  or  Michigan  Coal-field 68 

The  Illinois  Coal-basin. 69 

Indiana,  Western  Kentucky 69 

Illinois 70 

The  Missouri  Coal-basin 74 

Iowa. , 74 

Kansas 75 

A  rkansas 76 

Indian  Territory 77 

Texas,  Colorado 78 

Lignites  and  Lignitic  Coals  of  the  Western  States, 79 

Wyoming,  New  Mexico,  Arizona,  Utah 80 

Montana,  North  Dakota,  Nevada,  California 81 

Oregon,  Washington 82 

Alaska 83 

CHAPTER   V. 

TESTS   OF   THS   HEATING    VALUE    OF    AMERICAN   AND   FOREIGN   COALS. 

Johnson's  Tests  of  American  Coals 84 

Scheurer-Kestner's  Tests  of  European  Coals "84 

<jfruner's  Classes  of  Coals 87 

Comparison  of  Theoretical  and  Industrial  Heating  Power  of  Coals 88 

Remarks  on  Scheurer-Kestner's  Tests 89 

Mahler's  Tests  of  European  Coals 92 

Mahler's  Bomb-calorimeter 94 

Lord  and  Haas's  Tests  of  American  Coals 101 

Comparison  of  Mahler's  and  Lord  and  Haas's  Results • 110 

Heating  Value  of  Wyoming  Coals , Ill 

€alorific  Power  of  Weathered  Coals 113 

Weathering  of  Coal 116 

•Composition  and  Heating  Value  of  German  Coals 116 

Selection  of  Coal  for  Steam-boilers 119 

Appearances  for  Determining  Heating  Value  of  Coals 121 

Comparative  Calorimetric  Tests  of  Coals 126 

Testing  the  Relative  Value  of  Different  Coals 128 

CHAPTER   VI. 

FUELS    OTHER   THAN    COAL. 

<?oke <+ 131 

Pressed  Fuel  or  Briquettes 131 

Coal-dust..  .   132 


X  CONTENTS. 

PAGE. 

Peat  or  Turf 133 

Wood 134 

Sawdust 135- 

Tan-bark , 136 

Straw 136 

Bagasse 137 

Petroleum . . .  4 , 137 

Oil  versus  Coal  as  Fuel 141 

Gas  Fuel 142 

Corn  as  Fuel 144 


CHAPTER  VII. 

FURNACES. — METHODS  OF  FIRING. — SMOKE-PREVENTION.— MECHANICAL,  STOKERS. 

FORCED    DRAFT. 

Location  of  the  Furnace 145 

Requirements  of  a  Good  Furnace 146 

Burning  of  Anthracite  Coal 147 

Burning  Small  Sizes  of  Anthracite 148 

Comparative  Efficiency  of  Steam-  and  Fan-blowers 150 

Grate-bars 151 

Shaking-  and  Dumping-grates 153 

The  McClave  Grate 153 

The  Argand  Steam-blower 154 

How  to  Burn  Soft  Coal 155 

How  to  Avoid  Smoke. 156- 

Practical  Success  of  Smoke-prevention 157 

Requirements  of  a  Smoke-preventing  Furnace 158 

The  Coking  System  of  Firing 159 

The  Walker  Furnace 160 

Alternate  Firing , 1G1 

The  ' '  Wing-wall "  Furnace  162 

Introduction  of  Heated  Air  into  the  Furnace 163 

Downward-draft  Furnaces. 105 

Automatic  or  Mechanical  Stokers 1 66 

The  Vicars  Stoker 109 

The  Coxe  Stoker 170 

The  Playford  Stoker 171 

The  Babcock  &  Wilcox  Stoker 171 

The  Roney  Stoker  173 

The  Acme  Stoker 174 

The  Wilkinson  Stoker 176 

The  Murphy  Furnace 176 

The  American  Stoker 1 77 

The  Jones  Under- feed  Stoker 1 79 

Forced  Draft 179 

The  Howden  T!ot-a:r  System 181 


CONTENTS.  XI 

PAGB 

Retarders 181 

The  Ellis  &  Eaves  Hot-air  System 182 

Furnaces  for  Burning  Coal-dust 184 

Methods  of  Burning  Petroleum 184 

Bagasse  Burner 187 

CHAPTER   VIII. 

SOME     ELEMENTARY    PRINCIPLES    OF    BOILER     ECONOMY     AND     CAPACITY.  —  THE 
PLAIN   CYLINDER   BOILER. 

Capacity  of  a  Plain  Cylinder  Boiler 188 

Calculations  of  Fuel  Economy .  „ 191 

Capacity  Depends  on  Economy „,  192 

Loss  of  Economy  due  to  Insufficient  Heating  Surface ^ . . .  195 

Maximum  Possible  Economy , 196 

Loss  of  Heat  by  Radiation „ .  198 

Capacity  of  a  Plain  Cylinder  Boiler  at  Different  Rates  of  Driving 200 

Disadvantages  of  the  Plain  Cylinder  Boiler „ 200 

Saving  Waste  Heat  of  the  Plain  Cylinder  Boiler 202 

Use  of  a  Water-tube  Boiler  as  an  Addition  to  the  Plain  Cylinder  Boiler 202 

Modern  Boiler  Practice  in  the  Anthracite  Coal  Regions 204 

CHAPTER   IX. 

EFFICIENCY   OF   THE    HEATING    SURFACE. 

Statement  of  the  Problem , 205 

Radiation  Considered 210 

Calculation  of  the  Coefficients  from  Results  of  Boiler  Trials 215 

General  Formulas  for  Efficiency 218 

Interpretation  of  the  Equation 21 9 

The  Coefficient  a  as  a  Criterion  of  Boiler  Performance 220 

Effect  of  Variation  of  the  Conditions 221 

Effect  of  Heating  Value  of  the  Fuel = 224 

Loss  of  Efficiency  due  to  Steam  in  the^Gases 226 

Practical  Conclusions  from  the  Discussion 228 

Low  Temperature  of  Furnace  may  cause  High  Flue  Temperature.  .  , 232 

Relation  of  Furnace  Temperature  to  Heating  Surface  Required 238 

Blechynden's  Experiments  on  Transmission  of  Heat 235 

Durston's  Experiments  on  Transmission  of  Heat 239 

Effect  of  Circulation  on  Economy 240 

Efficiency  docs  Not  Depend  on  Type  of  Boiler 242 

CHAPTER   X. 

TYPES   OF    STEAM-BOILERS. 

Evolution  of  Different  Forms  of  Boiler 247 

Double-cylinder  Boiler 247 


Xll  CONTENTS. 

PAGE 

Two-flue  Boiler '. 248 

Evolution  of  the  Steam-boiler  in  France  and  England 248 

The  Elephant  Boiler 248 

The  Cornish  Boiler 248 

The  Lancashire  Boiler 248 

The  Galloway  Boiler 248 

The  Horizontal  Return-flue  Boiler 249 

The  Vertical  Tubular  Boiler 25 1 

The  Locomotive  Boiler 254 

The  Spotch  Marine  Boiler '. 255 

The  Water-tube  Boiler 257 

Early  Forms  of  Water-tube  Boiler 258 

More  Recent  Forms  of  Water-tube  Boiler 258 

Modern  Forms  of  Water-tube  Boiler 265 

Water-tube  Marine  Boilers 274 

Forms  of  Boiler  used  in  Different  Countries 277 


CHAPTER  XI. 

THE  HORSE-POWER  OP  A  STEAM-BOILER. — PROPORTIONS  OP  HEATING   AND  GRATE- 
SURFACE. — PERFORMANCE   OF   BOILERS. 

The  Horse-power  of  a  Steam-boiler 280 

Definitions  of  Boiler  Horse-power 281 

Measures  for  Comparing  the  Duty  of  Boilers 282 

Proportions  of  Grate  and  Heating  Surface  for  a  Given  Horse-power 282 

Heating  Surface 283 

Measurement  of  Heating  Surface 284 

Horse-power,  Builder's  Rating „ 285 

Grate-surface 285 

Areas  of  Flues  and  Gas-passages 288 

Air-passages  through  Grate-bars 288 

Performance  of  Boilers 289 

Range  of  Results  with  Anthracite  Coal 289 

CHAPTER  XII. 

POINTS   OF   A   GOOD   BOILER. 

Selecting  a  New  Type  of  Boiler ^ 292 

Economy  of  Fuel 29H 

Danger  of  Explosion 295 

Durability 29C 

Facility  for  Removal  of  Scale 298 

Water  and  Steam  Capacity 298 

Steadiness  of  Water-level 299 

Dryness  of  Steam 299 

Water  Circulation .• 299 


CONTENTS.  xill 

PAGft 

CHAPTER   XIII. 

BOILER  TROUBLES   AND   BOILER-USERS'    COMPLAINTS. 

Causes  of  Complaint , 301 

Poor  Draft 302 

Insufficient  Grate-surface  and  Poor  Coal 304 

Furnace  not  Adapted  to  Coal 304 

Bad  Setting  of  Boiler 305 

Leaks  of  Air  through  Brickwork 306 

Improper  Firing. 307 

Insufficient  Heating  Surface 311 

Bad  Water 313 

Corrosion,  Internal 313 

Use  of  Zinc  as  a  Remedy  for  Corrosion. 316 

Incrustation  and  Scale 317 

Boiler-compounds , 319 

Causes  and  Remedies  for  Incrustation 321 

The  Use  of  Boiler-compounds 322 

Chemical  Theory  of  Scale  Remedies 323 

External  Corrosion 328 

The  Life  of  a  Steam-boiler 328 

Defects  Discovered  by  Inspection 329 

Explosions  Caused  by  Hidden  Defects 329 

CHAPTER   XIV. 

EVAPORATION    TESTS    OF   STEAM-BOILERS. 

Object  of  an  Evaporation  Test 332 

Rules  for  Conducting  Boiler  Trials,  Code  of  1899 333 

Forms  for  Report  of  a  Trial 343 

Appendices  to  Code  of  1899 348 

Computation  of  the  Results  of  a  Boiler  Trial 376 

CHAPTER   XV. 

RESULTS   OF    STEAM-BOILER   TRIALS. 

Range  of  Economy  Found  in  Practice 380 

Spence's  Experiments  on  Varying  the  Air-supply 381 

Results  of  Tests  with  Small  Sizes  of  Anthracite  Coal 383 

Tests  of  Stirling  Boilers  with  Anthracite  Coal 386 

Comparative  Trials  of  Two-flue  Boilers  with  Pittsburg  Coal 392 

Tests  of  a  Babcock  &  Wilcox  Marine  Boiler 394 

Tests  of  a  Thornycrof t  Boiler 398 

Tests  at  the  Centennial  Exhibition .  402 


X1Y  CONTENTS. 

PAGE 

CHAPTER   XVI. 

PROPERTIES    OF   WATER    AND   STEAM. — FACTORS    OF    EVAPORATION. — CHIMNEYS. 

Properties  of  Water 406 

Weight  and  Heat-units  of  Water 407 

Properties  of  Steam 408 

Steam-table 411 

Factors  of  Evaporation 417 

Chimney-draft  Theory 422 

Hate  of  Combustion  due  to  Height  of  Chimney 425 

Table  of  Sizes  of  Chimneys 428 

CHAPTER  XVII. 

MISCELLANEOUS. 

Economizers 480 

Apparatus  for  Indicating  Furnace  Conditions 434 

The  Arndt  Econometer 435 

Flue-gas  Analyses  and  the  Heat  Balance 436 

Designing  Boilers  for  a  Street-railway  Plant 437 

Loss  of  Fuel  due  to  Banking  Fires 445 

Coal  used  in  Banking  Fires 446 

Steam-boiler  Economy  in  Electric-light  Stations 447 

Cost  of  Coal  per  Boiler  Horse-power 448 

Boiler-room  Labor 448 

Steam-boiler  Practice  of  the  Future...  449 


STEAM-BOILER  ECONOMY. 


CHAPTER  I. 
PKINCIPLES  AND  DEFINITIONS. 

A  Steam-boiler  is  a  vessel  in  which,  by  the  agency  of  heat  derived 
from  the  combustion  of  fuel,  water  is  converted  into  steam. 

The  study  of  the  operation  of  a  steam-boiler  includes  the  consider- 
ation of  the  following  subjects : 

1.  The  fuel,  its  kind,  quality,  and  chemical  composition. 

2.  The  air  supplied  to  the  fuel  to  effect  its  combustion  or  rapid 
oxidation ;  also  the  moisture  in  the  air. 

3.  The  furnace  in  which  the  combustion,  more  or  less  complete, 
takes  place ;  its  construction  and  its  fuel-burning  capacity. 

4.  The  loss  of  unburned  fuel  through  the  grate-bars  of  the  furnace, 
or  in  the  ashes  withdrawn  from  it. 

5.  The  heat  generated  by  the  combustion ;  its  quantity ;  the  temper- 
ature attained  in  and  beyond  the  furnace;  and  the  efficiency  of  the 
combustion,  or  the  ratio  which  the  quantity  of  heat  actually  generated 
bears  to  that  which  might  be  generated  with  perfect  combustion. 

6.  The  gaseous  products  of  combustion,  and  their  dilution  by  an 
excessive  supply  of  air. 

7.  The  transfer  of  heat  from  the  fire,  and  from  the  hot  gases  gener- 
ated by  the  combustion,  through  the  shell  or  tubes  of  the  boiler  into 
the  water,  and  the  conditions  which  increase  or  diminish  the  rate  and 
the   effectiveness  of  the  transfer. 

8.  The  loss  of  heat  due  to  the  escape  of  hot  gases  into  the  flue  or 
chimney. 

9.  The  loss  of  heat  due  to  radiation  from  the  external  surfaces  of 
the  furnace  and  boiler. 


2  STEAM-BOILER  ECONOMY. 

10.  The  properties  of  water  and  steam  at  different  temperatures. 

11.  The  capacity  of  the  boiler,  or  the  quantity  of  water  it  is  capa- 
ble of  converting  into  steam   under  certain  given  or  assumed  con- 
jtiitions. 

12.  The  efficiency  of  the  boiler,  or  the  ratio  of  the  heat  absorbed 
by  the  boiler  to  the  heat  which  would  be  generated  by  the  complete 
combustion  of  so  much  of  the  fuel  as  is  actually  burned. 

13.  The  efficiency  of  the  boiler  and  furnace  combined,  or  the  ratio 
of  the  heat  absorbed  by  the  boiler  to  the  heat  which  would  be  gener- 
ated by  complete  combustion  of  all  the  fuel  used,  including  that  lost 
through  the  grates  and  withdrawn  in  the  ashes. 

The  consideration  of  each  one  of  the  several  items  specified  above  is 
necessary  to  a  thorough  understanding  of  the  operation  and  the  fuel 
economy  of  a  steam-boiler,  and  each  will  be  discussed  at  length  in 
succeeding  chapters  of  this  book. 

The  general  subject  of  steam-boiler  economy,  however,  includes 
other  subjects  than  those  relating  to  fuel  economy,  such  as  the  con- 
struction of  the  boiler  in  its  relation  to  strength,  durability,  repairs, 
.facility  of  cleaning,  space  occupied,  first  cost,  cost  of  labor  for  its  oper- 
ation, etc.  These  will  also  be  treated  of  in  their  proper  place. 

Heat  is  a  form  of  energy  in  bodies,  supposed  to  consist  of  molec- 
ular vibration.  Its  nature,  like  that  of  gravity  and  electricity,  is  not 
clearly  understood,  but  its  effects  may  be  perceived  and  measured. 
Its  intensity  in  any  body  may  be  measured  in  degrees  of  temperature  by 
a  thermometer  or  pyrometer.  Its  quantity  may  be  measured  in  heat- 
units.  When  two  bodies,  one  hotter  or  at  a  higher  temperature  than 
the  other,  are  placed  in  contact,  there  is  a  flow  of  heat  from  the  hotter 
into  the  cooler  body,  tending  to  equalize  their  temperature,  and  the 
quantity  of  heat  thus  transferred  may  be  measured  or  estimated  if  the 
nature  or  composition,  the  weight,  and  the  temperature  of  the  two 
bodies  are  known.  One  or  both  the  bodies  may  experience  a  change 
of  state  by  reason  of  the  transfer  of  heat.  Thus  if  a  piece  of  ice  be 
plunged  into  a  vessel  containing  steam,  the  flow  of  heat  from  the 
steam  will  condense  it  into  water,  and  the  flow  of  heat  into  the  ice  will 
cause  the  latter  to  melt  and  be  changed  also  into  water. 

Temperature,  or  intensity  of  heat,  is  measured  in  degrees,  by  a  ther- 
mometer or  pyrometer.  Certain  fixed  or  standard  temperatures  are 
identified  by  certain  phenomena  of  the  change  of  state  of  certain 
bodies.  The  two  most  commonly  used  standard  temperatures  are:  (1) 
that  of  melting  ice,  zero  on  the  Centigrade  thermometric  scale  or  32° 


PRINCIPLES  AND  DEFINITIONS.  3 

oil  the  Fahrenheit  scale,  and  (2)  that  of  the  boiling-point  of  pure 
water  at  the  mean  atmospheric  pressure  of  14.7  Ibs.  per  square  inch, 
viz.,  100°  on  the  Centigrade  scale  or  212°  on  the  Fahrenheit  scale.  The 
Fahrenheit  scale  is  most  commonly  used  in  England  and  the  United 
States.  If  the  range  of  temperature  between  the  freezing  and  the 
boiling-points  of  water  be  divided  into  180  equal  parts,  we  obtain  the 
scale  of  degrees  of  the  Fahrenheit  thermometer,  which  scale  may  be 
extended  indefinitely  downwards  and  upwards  to  measure  the  lowest  and 
the  highest  temperatures  found  in  the  arts.  For  scientific  measure- 
ments of  great  accuracy  and  through  a  wide  range  degrees  of  temper- 
ature may  be  measured  by  the  air-thermometer,  in  which  the  recorded 
degree  of  temperature  is  proportional  to  the  product  of  the  pressure 
and  volume  of  a  given  weight  of  air.*  For  all  ordinary  purposes  the 
mercury  thermometer  is  available  between  the  range  of  —  40°  and  600° 
F. ,  and  mercury  thermometers  with  compressed  nitrogen  in  the  tube 
above  the  mercury  may  be  used  for  temperatures  as  high  as  900°  or 
1000°  F.  For  higher  temperatures,  up  to  3000°  F.,  the  Uehling  and 
Steinbart  air-pyrometer,  and  the  Chatelier  electric  pyrometer  are  avail- 
able. For  obtaining  the  temperature  of  chimney-gases,  from  300°  to 
1200°,  metallic  pyrometers  may  be  used,  but  their  indications  are  apt 
to  be  inaccurate. 

The  temperatures  commonly  observed  in  steam-boiler  practice  are, 
on  the  Fahrenheit  scale: 

1.  The   temperature   of   the  feed-water,   from  32°  to   300°  and 
upwards. 

2.  The  temperature  of  the  steam,  from  212°  to  400°  (correspond- 
ing to  saturated  steam  of  250  Ibs.  per  sq.  in.  absolute  pressure)  and 
upwards  (500°  or  over  for  highly  superheated  steam). 

3.  The    temperature   in   the   furnace,    from    1000°   to   3000°   or 
upwards. 

4.  The  temperature  of  the  escaping  flue-gases,  from  300°  to  1200° 
and  upwards. 

5.  Temperatures  of  the  gases  of  combustion,  taken  at  points  in 
the  gas-passages  through  the  boiler  intermediate  between  the  furnace 
and  the  flue.  s 

A  Heat-unit,  or  British  Thermal  Unit   (B.T.U.),  is  the  quantity 
of  heat  required  to  raise  the  temperature  of  one  pound  of  pure  water 


*  Consult  Rankine,  Steam-engine,  p.  226;  Kent's  Mecli.  Engrs.  Pocket-book, 
p.  454;  Trans.  A.  S.  M.  E.,  vol.  vi.  p.  282. 


4  STEAM-BOILER  ECONOMY. 

one  degree  Fahrenheit,  at  and  near  its  temperature  of  greatest  density, 
39.1°  F.  (Rankine). 

The  quantity  of  heat  required  to  raise  the  temperature  of  one 
pound  of  water  1°  F.  varies  very  slightly  with  the  temperature,  being 
nearly  constant  below  100°  F.  and  increasing  at  higher  temperatures, 
so  that  to  raise  its  temperature  from  32°  to  100°  requires  68.08 
instead  of  68  B.T.U.,  and  from  32°  to  212°,  180.9  instead  of  180 
B.T.U. 

The  Unit  of  Evaporation  (U.E.)  is  the  quantity  of  heat  required 
to  convert  one  pound  of  water  at  212°  into  steam  of  the  same  tem- 
perature. It  is  equivalent  to  965.7  B.T.U. 

Latent  Heat  is  the  quantity  of  heat  which  apparently  disappears 
(or  becomes  latent  or  hidden,  and  therefore  not  measurable  by  a 
thermometer)  when  a  body  changes  its  state  from  solid  to  liquid 
or  from  liquid  to  gaseous,  while  the  temperature  remains  constant. 
Thus  when  a  pound  of  ice  at  32°  is  converted  into  water  at  the  same 
temperature,  142  B.T.U.  becomes  latent,  and  when  a  pound  of  water 
at  212°  is  converted  into  steam  at  212°,  965.7  B.T.U.  (or  one  U.E.) 
becomes  latent. 

When  a  body  changes  its  state  from  the  gaseous  to  the  liquid 
form,  or  from  the  liquid  to  the  solid  form,  the  heat  which  was  latent 
is  given  off  and  becomes  sensible  heat.  Thus  a  pound  of  steam  at 
212°  in  condensing  to  water  at  212°  transfers  965.7  B..T.U.  to  sur- 
rounding bodies,  raising  their  temperature,  and  a  pound  of  water  at 
32°  freezing  into  ice  at  the  same  temperature  will  give  off  142  B.T.U. 
to  the  surrounding  atmosphere. 

Specific  Heat  is  a  figure  representing  the  quantity  of  heat,  ex- 
pressed in  thermal  units,  required  to  raise  the  temperature  of  one 
pound  of  any  given  substance  one  degree;  or  it  is  the  ratio  of  the 
quantity  of  heat  required  to  raise  the  temperature  of  a  given  weight 
of  the  substance  one  degree  to  the  quantity  required  to  raise  the  tem- 
perature of  the  same  weight  of  water  one  degree  at  its  temperature  of 
maximum  density.  The  specific  heat  of  water  at  39.1°  F.  being 
taken  at  unity,  that  of  all  other  known  substances,  except  hydrogen, 
is  less  than  unity. 

One  of  the  methods  of  determining  the  specific  heat  of  a  body  is 
the  method  by  mixture,  described  as  follows : 

The  body  whose  specific  heat  is  to  be  determined  is  raised  to  a 
known  temperature,  and  is  then  immersed  in  a  mass  of  liquid  of 
which  the  weight,  specific  heat,  and  temperature  are  known.  When 


PRINCIPLES  AND  DEFINITIONS.  5 

both  the  body  and  the  liquid  have  attained  the  same  temperature,  this 
is  carefully  ascertained. 

Now  the  quantity  of  heat  lost  by  the  body  is  the  same  as  the 
quantity  of  heat  absorbed  by  the  liquid. 

Let  c,  w,  and  t  be  the  specific  heat,  weight,  and  temperature  of  the 
hot  body,  and  c',  w',  and  t'  of  the  liquid.  Let  T  be  the  temperature 
the  mixture  assumes. 

Then,  by  the  definition  of  specific  heat,  c  X  w  X  (t  —  T)  =  heat- 
units  lost  by  the  hot  body,  and  c'  X  w'  X  (T  —  t')  =  heat-units  gained 
by  the  cold  liquid.  If  there  is  no  heat  lost  by  radiation  or  conduc- 
tion, these  must  be  equal,  and 

r'w'iT  _  /'\ 

cw(t  -  T)  =  c'w'(T-  t')    or    c  =  c-d-JJ. 


The  specific  heats  of  several  different  substances  at  ordinary 
atmospheric  temperatures  are  given  below  : 

SOLIDS. 

Copper  ......................  0.0951  Aluminum  ..............        0.2185 

Glass  ..............  ..........  0.1937  Charcoal  ................        0.2410 

Iron,  cast  ....................  0.1298  Coal  ....................  0.20  to  0.24 

Iron,  wrought  ................  0.1138  Coke  ...................        0.203 

Steel,  soft  ....................   0.1165  Brickwork  and  masonry.  .  about  0.20 

Platinum  .....................  0.0324  Wood  ..................  0.46  to  0.65 

LIQUIDS. 
Water  .......................  1.0000        Mercury  ................  _____  0.0333 

GASES. 

At  Constant    At  Constant 
Pressure.          Volume. 

Steam,  superheated  ............................  0.4805  0.346 

Air  ____  .  .................................  .....  0.2375  0.1686 

Oxygen  ......................................  0.2175  0.1551 

Hydrogen  ....................................  3.4090  24122 

Nitrogen  ....................................  0.2438  0.1727 

Carbon  monoxide,  CO  .........................  0.2479  0.1758 

Carbon  dioxide,  CO,  ...........................   0.217  0.1535 

Marsh-gas  (methane),  CH4  .....................  0.5929  0.4683 

Olefiunt  gas  (ethylene),  C2H4  ..............  ____   0.404  0.173 

Blast-furnace  gas  .............................  C.228 

Gases  in  chimneys  of  steam-boilers  (approximate)  0.240 

The  specific  heat  of  a  gaseous  mixture,  such  as  that  of  chimney- 
gas,  is  found  by  multiplying  the  percentage  of  each  of  the  constituent 
gases  by  the  specific  heat  of  that  gas  and  dividing  the  sum  of  the  prod- 


6  STEAM-BOILER  ECONOMY. 

nets  by  100.     Thus  for  a  gas  whose  composition  is  C02 ,  12;  CO,  0.5; 

O,  9.5;  N,  78,  we  have 

C0a 12        X     0.217     =     2.604 

CO 0.5     X     0.248     =     0.124 

O  9.5     X     0.2375=     2.256 

N 78        X    0.2438  =  19.016 

fooTo  2Ooo 

Whence  the  specific  heat  is 

24.0  -^  100  =  0.240. 

The  specific  heats  of  all  substances  in  the  solid  or  liquid  state 
increase  slowly  as  the  temperature  rises.  Experiments  by  Mallard 
and  Le  Chatelier  indicate  a  continuous  increase  in  the  specific  heat  of 
C0a ,  steam,  and  other  gases  with  rise  of  temperature.  The  variation 
is  inappreciable  at  212°  F.,  but  increases  rapidly  at  high  temperatures. 
In  the  absence  of  data  of  specific  heats  of  gases  at  high  temperatures, 
the  figures  given  in  the  above  tables  are  generally  used  in  calculations 
relating  to  gases  of  combustion,  although  their  use  may  lead  to  errors 
of  unknown  magnitude  in  the  results. 

The  following  figures,  showing  increase  of  specific  heat  of  metals 
with  rise  of  temperature,  are  sometimes  used  in  pyrometric  calculations : 

Platinum,  22°  to  440°  F.,  0.0332,  increasing  0.000305  for  each  100°  F.  above  440°. 

Copper,  32°  to  212° 0.094 

32°  to  572°... 0.1013 

"Wrought  iron,*  32°  to  200° 0.1129- 

32°  to  600° 0.1327 

32°  to  2000° 0. 2619 

The  Quantity  of  Heat  in  a  body,  in  British  thermal  units,  meas- 
ured above  a  certain  temperature  taken  as  standard,  usually  32°  F., 
is  the  product  of  its  weight,  its  average  specific  heat  between  the 
limits  of  temperature  considered,  and  the  difference  between  its  tem- 
perature and  the  standard  temperature.  Thus  the  quantity  of  heat 
above  32°  in  a  piece  of  wrought  iron  weighing  10  Ibs.,  at  a  tempera- 
ture of  212°,  is  10  X  .1138  X  (212  -  32)  =  204.84  B.T.U. 

This  statement  is  true,  however,  only  when  the  body  does  not 
change  its  state  between  the  standard  temperature  and  the  higher 
temperature.  When  the  body  changes  its  state,  its  latent  heat  must 
be  considered.  Thus  the  heat  above  32°  in  a  pound  of  steam  is  the 
sum  of 

Heat  required  to  raise  its  temperature  from  32°  to  212° 180.9  B  T.U. 

Latent  heat  of  evaporation  at  212° 965.7       " 

Total.. 


*  J.  C.  Hoadley,  Trans.  A.  S.  M.  E.,  vi.  713. 


PRINCIPLES  AND  DEFINITIONS.  7 

The  quantity  of   heat   in   a   pound  of   saturated   steam  at   320°  F. 
(75.3  Ibs.  gauge  pressure  per  sq.  in.)  is 

Heat  (above  32°)  in  water  at  320° 291.2  B.T.U. 

Latent  heat  of  evaporation  at  320°  888.4       " 

Total 1179:6       " 

When  the  steam  is  superheated,  the  quantity  of  heat  required  for 
superheating  must  be  added.  Thus  if  the  steam  of  75.3  Ibs.  gauge 
pressure,  whose  temperature  when  saturated  is  320°,  be  superheated, 
while  its  pressure  remains  constant,  to  420°,  the  increase  of  100°  of 
temperature  will  require,  since  the  specific  heat  of  superheated  steam 
at  constant  pressure  is  0.48,  an  addition  of  48  B.T.U. ,  making  the 
total  heat  1179.6  +  48=1227.6  B.T.U.  The  properties  of  steam 
will  be  discussed  further  in  another  chapter. 

Heat  of  Combustion. — Every  combustible  chemical  element,  such 
as  carbon,  hydrogen,  and  sulphur,  and  every  gaseous  fuel  of  definite 
chemical  composition,  containing  two  or  more  elements,  such  as 
carbon  monoxide  (CO)  and  methane  (marsh-gas,  CH4),  when  com- 
pletely burned  in  oxygen  or  in  air  generates  a  definite  quantity  of 
heat  per  pound  of  the  combustible,  which  quantity  may  be  ascertained 
with  a  close  approximation  to  accuracy  by  means  of  an  instrument 
known  as  a  fuel  calorimeter.  The  exact  determination  of  the  heat  of 
combustion,  or  calorific  value,  of  any  combustible  requires  a  very 
delicate  apparatus,  a  high  degree  of  skill  on  the  part  of  the  operator, 
and  an  allowance  for  certain  unavoidable  errors,  such  as  loss  by  radia- 
tion, so  that  the  calorific  values  of  different  combustibles  as  reported 
by  different  authorities  show  a  slight  variation.  Thus  the  heating 
value  of  carbon  is  14,544  B.T.U.  according  to  Favre  and  Silbermann, 
and  14,647  B.T.U.  according  to  Berthelot.  That  of  hydrogen  is 
62,032  B.T.U.  according  to  Favre  and  Silbermann,  and  61,816  B.T.U. 
according  to  Thomsen.  The  round  figures  of  14,600  B.T.U.  for 
carbon  (burned  to  carbon  dioxide)  and  62,000  B.T.U.  for  hydrogen 
(burned  to  steam  and  the  steam  condensed  to  liquid  water)  are  gen- 
erally used  in  calculations  relating  to  steam-boiler  practice. 

The  heating  value  of  any  fuel,  such  as  coal,  consisting  of  a  mixture 
of  combustible  and  non-combustible  substances  may  be  directly  deter- 
mined by  means  of  a  calorimeter,  or  it  may  be  calculated  from  its 
ultimate  chemical  analysis  by  Dulong's  formula,  which  is: 

Heating  value  =  -^  X   i~14,600  C  -f  62,000  (H  -  5)  +  4000  si, 
iUU         |_  \  o  /  _j 


8  STEAM-BOILER  ECONOMY. 

in  which  C,  H,  0,  and  S  are  the  percentages  of  carbon,  hydrogen, 
oxygen,  and  sulphur  in  the  coal,  as  determined  by  analysis. 

Combustion  of  Fuel. — Combustion  may  be  perfect  or  imperfect, 
depending  upon  the  supply  of  air  in  the  furnace  and  upon  other  con- 
ditions which  will  be  discussed  later.  When  the  combustion  is  perfect 
the  whole  of  the  carbon  in  the  fuel  is  burned  to  carbon  dioxide,  CO, , 
each  pound  generating  14,600  B.T.U.,  and  the  whole  of  the  hydrogen 
is  burned  to  steam,  or  vapor  of  water,  H,0,  each  pound  generating 
62,000  B.T.U.  Part  of  the  heat  of  the  combustion  of  hydrogen  is 
absorbed  in  the  latent  heat  of  evaporation  of  the  9  Ibs.  of  steam 
formed  by  the  combustion  of  1  Ib.  of  hydrogen,  and  another  part  in 
superheating,  to  the  temperature  of  the  furnace,  this  steam,  and  also 
the  steam  that  may  be  derived  from  moisture  in  the  coal  or  in  the  air 
supplied  to  the  furnace. 

When  the  combustion  is  imperfect  part  of  the  carbon  may  be 
burned  only  to  carbon  monoxide,  CO,  generating  only  4450  B.T.U. 
per  pound;  or  part  of  the  carbon  which  has  been  burned  on  the  grate 
to  CO,  may  be  "unburned,"  being  converted  into  CO  on  passing 
through  a  bed  of  red-hot  coke,  absorbing  carbon  therefrom  by  the 
chemical  reaction  CO,  -f-  C  =  2CO,  a  cooling  process,  absorbing  10,150 
B.T.U.  per  pound  of  the  C  originally  burned  to  CO,.  Also,  in  im- 
perfect combustion  some  of  the  hydrogen,  together  with  the  carbon 
with  which  it  is  combined  in  the  coal,  forming  the  "  volatile  matter," 
may  be  only  distilled  from  the  coal  and  not  burned,  or  the  hydrogen 
only  in  this  volatile  matter  may  be  burned,  leaving  the  carbon,  in  the 
form  of  soot  or  smoke,  to  be  carried  off  in  the  gases  passing  out  of  the 
furnace.  All  of  the  products  of  imperfect  combustion,  the  carbon 
monoxide,  the  hydrocarbon  gases  distilled  from  the  coal,  and  the  soot 
or  smoke,  may  afterwards  be  burned  if  they  are  carried  into  a  very 
hot  chamber,  where  they  are  brought  in  contact  with  a  sufficient  supply 
of  highly  heated  air. 

How  Smoke  may  be  Burned. — This  last  statement  is  contrary  to 
that  made  by  Charles  Wye  Williams  in  his  treatise  "  On  the  Combus- 
tion of  Coal  and  the  Prevention  of  Smoke,"  first  printed  about  sixty 
years  ago,  and  copied  extensively  by  later  writers,  viz.,  that  "When 
smoke  is  once  produced  in  a  furnace  or  flue,  it  is  as  impossible  to 
burn  it  or  convert  it  to  heating  purposes  as  it  would  be  to  convert  the 
smoke  issuing  from  the  flame  of  a  candle  to  the  purposes  of  heat  or 
light."  The  error  of  the  statement  made  by  Mr.  Williams  can  be 
easily  shown  by  a  simple  experiment  which  has  been  made  by  the 


PRINCIPLES  AND  DEFINITIONS.  9 

author.  A  short  piece  of  candle  was  placed  inside  of  a  tall,  narrow  tin 
cylinder.  The  deficient  supply  of  air  the  candle  thus  received  caused  it 
to  give  off  a  column  of  black  smoke.  This  was  caused  to  pass  into  the 
central-draft  tube  of  a  "Rochester  "  kerosene  lamp,  and  as  it  passed 
up  into  the  flame  of  the  lamp  it  was  completely  burned,  not  a  trace  of 
smoke  being  visible  in  the  lamp-chimney.  The  experiment  was  also 
made  with  a  still  larger  column  of  smoke,  produced  by  burning  paper 
under  the  lamp,  with  the  same  result. 

Flame  is  a  mass  of  intensely  heated  combustible  gas.  It  is  not 
necessarily  gas  in  a  state  of  combustion,  for  combustion  cannot  take 
place  without  access  of  air,  and  flame  may  exist,  as  in  passing  through 
a  furnace  or  flue,  where  there  is  no  supply  of  air  to  burn  the  gas.  If 
the  flame  in  passing  through  a  tube  becomes  cooled  below  a  bright  red 
heat,  the  gas  will  not  burn  when  it  escapes  and  comes  in  contact  with 
cool  air,  but  will  be  chilled  and  pass  off  as  uuburued  gas  and  smoke. 

The  flame  of  pure  hydrogen  gas  is  almost  invisible,  but  visibility 
and  color  may  be  given  to  it  by  the  presence  of  other  substances;  thus 
carbon  will  make  it  white,  copper  green,  cyanogen  purple,  and  sodium 
yellow. 

The  white  color  of  the  flame  of  hydrocarbon  gas,  such  as  that  from 
a  candle  or  that  of  a  kerosene  lamp,  is  due  to  intensely  heated  particles 
of  carbon.  If  the  flame  is  caused  to  impinge  on  a  cold  surface,  some 
of  these  particles  will  be  deposited  as  soot. 

Visible  flame  is  evidence  of  imperfect  combustion  or  non-combus- 
tion. The  product  of  the  perfect  combustion  of  carbon  is  invisible 
carbon  dioxide  gas,  and  that  of  hydrogen  is  invisible  vapor  of  water. 

Take  a  lighted  central-draft  kerosene  lamp  and  adjust  the  wick  to 
such  a  point  that  the  lamp  gives  a  rather  short  and  clear  white  light 
without  a  trace  of  smoke.  Now,  without  altering  the  adjustment  of 
the  wick,  gradually  obstruct  the  opening  at  the  bottom  of  the  central- 
draft-tube  and  observe  the  result.  The  flame  grows  longer  and  its 
whiteness  changes  to  yellow  and  then  to  red.  It  begins  to  smoke,  and 
finally  when  the  supply  of  air  is  nearly  shut  off  the  flame  has  risen  to 
nearly  the  top  of  the  chimney  and  a  dense  column  of  black  smoke  and 
soot  is  given  off.  We  learn  from  this  experiment  that  with  the  same 
consumption  of  fuel,  i.e.,  the  oil  supplied  by  the  wick,  the  flame  may 
be  short  and  intensely  hot,  or  very  long,  of  a  low  temperature,  smoky 
and  sooty.  While  the  flame  is  lengthening  and  before  it  becomes  smoky 
the  combustion  may  be  complete,  but  it  is  not  effected  in  as  short  a  space 
as  it  was  with  the  original  supply  of  air.  For  a  given  supply  of  fuel 


10  STEAM-BOILER  ECONOMY. 

a  short  flame  means  rapid  and  complete  combustion,  a  longer  flame 
delayed  combustion,  and  a  very  long  flame  imperfect  combustion.  If 
midway  in  the  flame  of  medium  length  a  cool  surface  be  interposed, 
the  temperature  of  the  flame  will  be  lowered,  the  combustion  will  be 
rendered  imperfect,  and  smoke  and  soot  will  be  produced. 

The  principles  learned  from  these  simple  experiments  with  the  flame 
of  a  lamp  are  of  great  importance  in  connection  with  the  study  of  the 
action  of  steam-boiler  furnaces. 

A  Transfer  of  Heat  from  the  burning  fuel  and  from  the  hot  gases 
produced  by  its  combustion  into  the  water  contained  in  a  steam-boiler 
takes  place  through  the  metal  plates  and  tubes  of  the'  boiler  in  two 
ways:  (1)  by  radiation  directly  from  the  fire  and  from  the  hot  par- 
ticles of  carbon  in  the  flame,  and  (2)  by  contact  of  the  hot  gases  with 
the  metal  of  the  boiler.  The  laws  of  these  two  methods  of  transfer  are 
as  yet  imperfectly  understood,  and  there  is  a  great  lack  of  accurate 
scientific  data  concerning  them.  The  experimental  determination  of 
these  data  is  a  matter  of  extreme  difficulty,  on  account  of  the  number 
of  variable  conditions  attending  the  experiments.  Such  conditions  are : 
the  extent  of  surface  exposed  to  direct  radiation;  the  temperature  of 
the  radiating  surfaces,  the  resistance  to  radiation  of  metal  plates  in  dif- 
ferent conditions,  more  or  less  coated  with  scale  and  soot;  the  manner 
in  which  the  heated  gases  impinge  upon  the  shell  and  tubes;  the  triple 
resistance  to  transfer  of  heat  from  the  gases  to  the  water,  viz.,  the  re- 
sistances of  the  external  and  internal  surfaces  of  the  metal,  varying  with 
their  condition,  and  the  resistance  of  the  metal  between  these  surfaces, 
varying  with  the  nature  of  the  metal  and  its  thickness;  the  influence 
which  the  temperature  of  the  gases  on  one  side  of  the  plate  and  tubes, 
steadily  decreasing  as  they  pass  from  the  furnace  to  the  flue,  and  the 
temperature  of  the  water  on  the  other,  sensibly  constant,  have  upon  the 
rate  of  transfer  of  heat  through  the  metal  and  its  exterior  and  interior 
surfaces.  Notwithstanding,  however,  the  lack  of  accurate  knowledge 
concerning  the  influence  of  these  several  variables  on  the  transfer  of 
heat  in  steam-boilers,  enough  is  known  to  enable  us  to  deduce  some 
broad  general  laws,  and  to  express  some  of  them  in  empirical  formulae, 
so  that  boilers  may  intelligently  be  designed  to  fill  given  requirements,, 
and  so  that  the  probable  performance  of  any  boiler  and  furnace  may 
be  predicted  from  a  study  of  its  design  and  dimensions,  when  the  char- 
acter of  the  fuel  is  known,  within  limits  of  error  sufficiently  narrow  for 
practical  purposes. 

The  Capacity  of  a  Boiler  is  its  capacity  for  producing  steam.     It 


PRINCIPLES  AND  DEFINITIONS.  11 

may  be  expressed  in  the  number  of  heat-units  absorbed  by  the  boiler  in 
a  given  time,  such  as  one  second,  or  in  the  number  of  pounds  of  water 
converted  into  steam  in  an  hour. 

"  Equivalent "  Evaporation. — Since  the  latter  number  will  depend 
upon  the  temperature  of  the  feed-water  and  upon  the  pressure  or  tem- 
perature of  the  steam,  it  is  customary  to  express  the  capacity  in  terms 
of  what  is  called  "  equivalent  evaporation,"  that  is,  reducing  the 
number  of  pounds  of  steam  actually  generated  at  a  given  or  observed 
pressure  from  feed-water  of  an  observed  temperature,  into  the  equiva- 
lent evaporation  per  hour  from  feed-water  of  212°  into  steam  at  the 
same  temperature,  or,  as  it  is  commonly  expressed,  "  equivalent 
evaporation  per  hour  from  and  at  212°." 

The  evaporation  of  a  pound  of  water  from  and  at  212°  being  the 
"unit  of  evaporation"  (U.E.),  equal  to  965.7  B.T.U.,  the  capacity  of 
a  boiler  may  be  stated  as  so  many  U.E,  per  hour. 

Boiler  Horse-power. — Another  convenient  method  of  expressing 
the  capacity  of  a  boiler  is  in  terms  of  "  Boiler  Horse-power,"  a  boiler 
horse-power  being  equal,  according  to  a  commonly  accepted  conven- 
tion,- to  34|  U.E.  per  hour,  or  34-^  Ibs.  of  water  evaporated  from  and 
at  212°  per  hour.  This  latter  is  the  usual  method  of  expressing  the 
capacity  of  stationary  boilers  in  the  United  States.  It  is  not  used  for 
marine  or  locomotive  boilers. 

A  boiler  rated  at  100  H.P.  would  therefore  be  rated  also  at  a 
capacity  of  3450  Ibs.  of  water  from  and  at  212°  per  hour,  or  at 
3,331,665  B.T.U.  per  hour,  or  925.5  B.T.U.  per  second.  The  B.T.U. 
rating  is  not  used  in  practice,  as  it  is  not  so  convenient  as  the  other 
methods  of  rating. 

It  is  to  be  noted  that  the  "rating"  of  a  boiler  as  100  H.P.  may 
be  very  different  from  the  actual  capacity  it  may  show  under  a  given 
set  of  conditions.  The  "rating"  is  supposed  to  be  its  average  capacity 
under  easy  conditions  of  driving,  with  fairly  good  fuel,  and  with 
ordinary  draft.  Two  boilers  exactly  alike  in  all  respects  may  both  be 
rated  at  100  H.P.,  and  one  of  them  with  excellent  fuel  and  forced 
draft  may  be  actually  developing  200  H.P.,  while  the  other,  with  poor 
fuel  or  insufficient  draft  or  both,  may  not  be  capable  of  developing 
over  75  H.P. 

The  Efficiency  of  a  Boiler  may  mean:  1.  The  ratio  of  the  heat 
absorbed  by  it  to  the  heat  actually  generated  in  the  furnace;  2.  The 
ratio  of  the  heat  absorbed  by  it  to  the  heating  value  of  the  combustible 
actually  burned  (whether  thoroughly  or  not) ;  3.  The  ratio  of  the 


12  STEAM-BOILER  ECONOMY. 

heat  absorbed  by  it  to  the  heating  value  of  the  fuel  supplied  to  the 
furnace,  whether  all  the  fuel  is  burned  or  not  (some  of  the  fuel  may 
fall  through  the  grates  or  be  withdrawn  with  the  ashes,  and  not  be 
burned).  The  first  of  these  efficiencies  is  not  used  in  practice,  for  the 
reason  that  there  is  no  convenient  way  of  estimating  the  amount  of 
heat  actually  generated  in  the  furnace,  or  of  determining  what  portion 
of  the  fuel  is  imperfectly  burned.  The  second  and  third  are  com- 
monly used  and  are  thus  denned: 

Heat  absorbed  per  Ib.  combustible 

Efficiency  of  the  boiler  =  ^ — r. —  — ^ g      „       — =- — prr-. 

Heating  value  of  1  Ib.  combustible 

T^  •  *  j.u    u  -i  Heat  absorbed  per  Ib.  coal 

Efficiency  of  the  boiler  and  grate  =  == — -. —  x, .,   .. _. 

Heating  value  of  1  Ib.  coal 

The  meaning  of  the  word  "combustible"  in  the  above  definitions 
is  that  portion  of  the  total  fuel  supplied  to  the  furnace  which  remains 
after  deducting  its  moisture  (determined  by  a  test  of  a  sample)  and 
the  total  amount  of  ash  and  refuse  (including  unburned  coal)  with- 
drawn from  the  furnace,  through  the  grates  or  otherwise.  In  other 
words  it  is  the  sum  of  the  fixed  carbon  and  the  volatile  combustible 
matter,  or  the  "coal  dry  and  free  from  ash." 

The  Operation  of  a  Steam-boiler. — The  several  events  that  take 
place  in  the  operation  of  an  ordinary  steam-boiler  may  be  briefly 
described  as  follows:  Consider  that  the  furnace  is  already  heated,  a 
hot  fire  of  partially  burned  coal  or  coke  lying  on  the  grate,  and  that 
the  boiler  is  delivering  steam  as  usual.  A  few  shovelfuls  of  fresh  coal 
are  evenly  spread  over  the  bed  of  hot  coal,  to  replenish  the  fire.  The 
first  thing  that  then  takes  place  is  the  evaporation  of  the  moisture 
contained  in  the  fresh  coal.  This  absorbs  heat  from  the  fire,  cooling 
it  for  a  short  time.  If  the  fresh  coal  is  of  small  size,  it  partly  fills  the 
interstices  between  the  pieces  of  hot  coal,  and  thereby  checks  the 
draft  and  diminishes  the  supply  of  air  which  enters  through  the 
grate.  The  formation  of  the  steam  by  the  evaporation  of  the  moisture 
in  the  fuel,  together  with  the  reduction  of  the  air-supply,  may  cause 
two  chemical  actions  to  take  place  which  are  in  the  nature  of  "de- 
composition" or  the  reverse  of  combustion  or  rapid  oxidation,  both  of 
which  are  detrimental  to  the  most  economical  operation  of  the  boiler. 
The  first  is  the  decomposition  of  the  carbon  dioxide,  formed  by  the 
union  of  the  oxygen  of  the  air  with  the  carbon  of  the  hot  coal  lying 
next  to  the  grate-bars,  into  carbon  monoxide,  by  the  reaction  C02  -f  0 
=  2CO,  which  takes  place  when  carbon  dioxide  is  passed  through  a 


PRINCIPLES  AND   DEFINITIONS.  13 

bed  of  very  hot  coal  or  coke,  the  supply  of  air  being  deficient.  The 
second  is  the  decomposition  of  a  portion  of  the  steam  produced  by  the 
evaporation  of  the  moisture  in  the  coal,  by  the  reaction  H20  -j-  0 
=  2H  -j-  CO,  which  takes  place  when  steam  is  brought  in  contact  with 
very  hot  carbon.  Both  of  these  reactions  or  decompositions  are  cool- 
ing processes,  absorbing  heat  from  the  fire,  and  they  therefore  dimin- 
ish the  rate  of  transfer  of  heat  through  the  heating  surface  of  the 
boiler.  Moreover,  they  both  rob  the  bed  of  fuel  of  some  of  its  carbon, 
converting  it  into  combustible  gases  which  may  escape  unburned,  thus 
causing  a  loss  of  heat.  Fortunately  the  length  of  time  during  which 
these  reactions,  unfavorable  to  economy,  take  place  is  not  long  when 
the  firing  is  done  carefully,  and  the  fresh  coal  is  fired  only  in  small 
quantities  at  a  time. 

After  the  moisture  is  driven  off  from  the  coal  the  volatile  matter 
begins  to  be  distilled,  and  this  continues  until  the  fresh  coal  has 
attained  a  red  heat.  When  the  amount  of  this  volatile  matter  is 
small,  when  the  air-supply  is  sufficient,  and  when  the  furnace  is  at  a 
high  temperature,  it  may  all  be  completely  burned  before  it  passes  out 
of  the  furnace;  but  if  it  is  distilled  in  large  volume  and  is  not  brought 
into  intimate  mixture  with  air  at  a  temperature  high  enough  to  main- 
tain ignition,  more  or  less  of  it  will  escape  unburned. 

After  the  volatile  matter  has  been  driven  off,  the  combustion  of 
the  remainder  of  the  coal  or  coke  is  completed.  If  the  relation  of  the 
thickness  of  the  bed  of  coal  on  the  grate  to  the  force  of  the  draft  is 
such  that  only  so  much  air  passes  through  the  grate  as  will  cause  the 
complete  combustion  of  the  carbon  to  C02 ,  the  temperature  of  the 
furnace  will  be  very  high,  a  most  favorable  condition  for  economy  of 
the  boiler.  If  the  force  of  the  draft  be  excessive,  in  relation  to  the 
resistance  of  the  grate  and  the  fuel  upon  it  to  the  passage  of  air,  or  if 
the  bed  of  coal  be  too  thin,  an  excessive  supply  of  air  will  pass  into 
the  furnace,  lowering  its  temperature  and  making  conditions  unfavor- 
able to  economy.  If,  on  the  other  hand,  the  thickness  of  the  bed  of 
coal  is  too  great  in  its  relation  to  the  force  of  the  draft,  or  the  draft  is 
insufficient,  the  air  supplied  to  the  furnace  will  not  be  enough  to 
secure  complete  combustion,  part  of  the  carbon  will  be  burned  only  to 
CO,  and  the  furnace  temperature  will  be  low.  In  this  case  there  is 
thus  a  twofold  loss  of  economy:  first,  that  due  to  direct  loss  of  heat- 
units  by  imperfect  combustion;  and  second,  that  due  to  low  furnace 
temperature,  which  lessens  the  rate  of  transfer  of  heat  into  the  boiler. 

While  the  coal  is  being  burned  as  above  described  it  generates  a 


14  STEAM-BOILER  ECONOMY. 

quantity  of  heat,  more  or  less  according  to  the  degree  of  completeness 
of  combustion,  at  a  rate  varying  from  one  instant  to  another  as  the 
conditions  vary,  the  coal  giving  off  moisture  at  one  period,  distilling 
its  volatile  matter  at  another,  and  having  its  carbon  burned  more  or 
less  perfectly  at  another.  The  temperature  of  the  furnace  also  varies 
as  these  conditions  vary,  and  with  it  the  rate  of  transfer  of  heat  into 
the  boiler  both  by  radiation  and  by  conduction. 

A  portion  of  the  heat  generated  in  the  furnace  being  radiated 
directly  from  it  into  the  boiler,  and  a  very  small  portion  escaping 
by  radiation  through  the  walls  of  the  furnace  (if  it  is  not  enclosed 
in  the  boiler  itself,  as  in  internally  fired  boilers),  the  remainder 
of  the  heat  passes  out  of  the  furnace  in  the  heated  gases  of  com- 
bustion. These  give  up  to  the  boiler  a  portion  of  their  heat  as 
they  pass  along  the  heating  surfaces,  and  carry  what  remains  into  the 
flue  leading  to  the  economizer  or  to  the  chimney,  as  the  case  may  be. 
How  much  of  this  heat  shall  be  absorbed  by  the  boiler  and  how  much 
shall  pass  into  the  chimney  depends  upon  a  number  of  variable  con- 
ditions which  will  be  discussed  later. 

Efficiency  of  the  Heating  Surface. — The  two  principal  sources  of 
loss  of  heat  in  the  ordinary  operation  of  a  steam-boiler  are:  1.  The  loss 
due  to  imperfect  combustion;  2.  The  loss  of  heat  in  the  chimney-gases. 

If  Hl  represents  the  heat-units  in  1  Ib.  of  the  gases  of  combustion 
in  the  furnace,  and  H9  the  heat-units  in  the  same  quantity  of  the  same 
gases  as  they  leave  the  boiler,  the  efficiency  of  the  heating  surface 
is  represented  by  the  equation 

tf    _    ffi  ~  ffi>  /i\ 

—g-.  .     .    .    .    .    .    .    (l) 

If  3T,  represents  the  temperature  of  the  gases  in  the  furnace,  and 
T,  their  temperature  as  they  leave  the  boiler,  the  efficiency  is  also  rep- 
resented by  the  equation 

T  —  T 

E  =  -^TT' (2) 

on  the  assumption  that  the  specific  heat  of  the  gases  is  the  same  at 
each  of  the  two  temperatures. 

From  equation  (2)  we  learn  that  the  efficiency  of  the  heating  sur- 
face may  be  increased  either  by  increasing  Tl  or  by  decreasing  3Ta  or 
by  both.  Therefore  high  efficiency  depends  both  on  high  furnace 
temperature  and  on  low  chimney  temperature.  How  to  increase  the 
furnace  temperature,  and  how,  with  increased  furnace  temperature,  to 


PRINCIPLES  AND  DEFINITIONS.  15 

decrease   the  chimney  temperature,   are   the   principal   things  to  be 
learned  in  regard  to  the  fuel  economy  of  steam-boilers. 

The  efficiency  of  the   heating  surface  corresponding  to  different 
temperatures  Tv  and  T^  is  shown  in  the  following  table : 


T,  = 


Ta  =  300° 
400°. 
500° 
600°. 
700°. 
800°. 
900°, 
1000°, 


2500° 

2000° 
-Efficiency, 

85 

1500° 
per  cent, 
80 

1000' 
70 

88 

84 

80 

73.3 

60 

80 

75 

66.7 

50 

76 

70 

60 

40 

72 

65 

53.3 

30 

68 

60 

46.7 

20 

64 

55 

40 

10 

60 

50 

33.3 

0 

The  highest  figure  of  efficiency  in  the  above  table,  88$,  it  is  scarcely 
possible  to  realize  in  practice  except  under  unusual  conditions,  such  as 
the  supplying  of  the  furnace  with  hot  air  heated  by  the  utilization  of 
some  of  the  heat  of  the  escaping  chimney-gases.  The  lowest  figure,  0$, 
represents  an  impossible  condition,  that  of  no  transfer  of  heat  from  the 
gases  into  the  boiler. 

The  principles  briefly  outlined  in  this  chapter  form  the  basis  of  the 
theory  of  the  economy  of  fuel  in  steam-boilers.  They  will  all  be  con- 
sidered in  greater  detail,  with  reference  to  experimental  data,  in  suc- 
ceeding chapters. 


CHAPTER  II. 
FUEL  AND  COMBUSTION. 

Chemistry  of  Fuel  and  of  Combustion. — The  four  principal  chem- 
ical elements  found  in  fuel  and  in  the  air  used  for  its  combustion  are 
carbon,  hydrogen,  oxygen,  and  nitrogen.  The  chemical  symbols  and 
the  atomic  weights  of  these  four  elements  are  respectively  C,  12;  H, 
1;  0,  16;  N,  14.  The  atomic  weights,  *or  combining  numbers,  are 
the  relative  proportions  by  weight  in  which  the  elements  always  com- 
bine with  each  other  to  form  definite  chemical  compounds.  Some  of 
these  compounds  are  the  following: 

Parts  by  Weight, 

Water,  H20 2H+  16O  =  18HaO 

Carbon  monoxide,  CO 12C  -f  16O  =  28CO 

Carbon  dioxide,  CO, 12C  -f  320  =  44CO9 

Methane,  CH4 12C  +    4H  =  16CH« 

The  names  of  the  last  three  compounds  are  those  used  in  modern 
works  on  chemistry.  Their  older  names  are:  CO,  carbonic  oxide j 
C02,  carbonic  acid ;  CH4,  marsh-gas,  or  light  carburetted  hydrogen. 

Air  is  not  a  chemical  compound,  but  a  mixture  of  oxygen  and 
nitrogen. 

Water-gas  (pure),  2H  -f-  CO,  is  a  mixture  of  two  parts  hydrogen  and 
28  parts  carbon  monoxide. 

Carbon  is  found  in  the  pure  and  solid  state  in  the  diamond,  in 
charcoal,  and  in  graphite.  Combined  with  hydrogen  it  is  found  in 
various  oils,  tars,  and  gases.  Combined  with  hydrogen  and  oxygen  it 
is  found  in  the  whole  range  of  vegetable  products.  It  is  the  principal 
constituent  of  coal  and  of  most  other  fuels,  whether  solid,  liquid,  or 
gaseous. 

Hydrogen  is  a  very  light  combustible  gas,  of  only  about  -^  of 
the  density  of  air.  It  may  be  produced  in  its  pure  gaseous  state  by 
the  electrical  or  chemical  decomposition  of  water.  It  is  also  formed, 
mixed  with  carbon  monoxide,  when  steam  is  passed  through  a  body  of 
white-hot  carbon,  the  chemical  reaction  being  thus  expressed : 

16 


FUEL  AND   COMBUSTION.  17 

H50  +  0    =  211  +  CO. 

2  +  16  +  12  =      2  +  28  parts  by  weight. 

18  parts  steam  +  12  parts  carbon  —  30  parts  water  gas. 

Hydrogen  is  a  constituent  of  most  fuels,  solid,  liquid,  and  gaseous, 
combined  either  with  carbon  or  with  both  carbon  and  oxygen  in 
various  proportions. 

Oxygen  is  an  invisible  gas,  16  times  as  heavy  as  hydrogen.  It  is 
found  in  the  gaseous  state,  mixed  with  nitrogen,  in  air.  Combined 
with  -J-  of  its  weight  of  hydrogen  it  forms  water.  It  is  the  universal 
supporter  of  combustion,  and  is  the  active  agent  of  corrosion  or  rust- 
ing, forming  oxides  of  the  metals.  It  is  found  combined  with  hydro- 
gen and  carbon  in  wood  and  other  vegetable  products,  forming  about 
40  per  cent  of  the  weight  of  dry  wood;  and  it  is  found  in  coal  in 
proportions  varying  from  1  per  cent  or  less  in  anthracite  to  over  25 
per  cent  in  lignites. 

Nitrogen  is  also  an  invisible  gas,  14  times  as  heavy  as  hydrogen. 
It  has  so  little  chemical  affinity  for  other  substances  that  it  cannot 
easily  be  combined  with  them  by  ordinary  chemical  methods.  The 
fixation  of  the  nitrogen  of  the  air,  or  causing  it  to  combine  with 
alkalies  to  form  fertilizers,  is  one  of  the  great  unsolved  problems  of  the 
chemist.  It  is  the  diluent  of  oxygen  in  air,  restraining  its  activity,  and 
causing  combustion  and  corrosion  to  be  less  rapid  than  if  they  were 
effected  in  pure  oxygen.  It  is  one  of  the  chief  causes  of  loss  of  heat  in 
the  operation  of  steam-boilers,  since  it  enters  the  furnace  at  the  tem- 
perature of  the  atmosphere  and  escapes  in  the  chimney-gases  at  a  high 
temperature.  It  is  found  in  all  coals,  usually  to  the  extent  of  from 
0.5  to  2  per  cent  of  their  weight.  When  coal  is  distilled  this  nitrogen 
appears  in  the  vapors,  combined  with  hydrogen,  as  ammonia,  NH3, 
and  when  the  coal  is  burned  the  NH3  is  decomposed  and  part  of  the 
N  is  oxidized  to  nitric  acid,  HN03. 

Sulphur  is  found  in  most  coals,  in  amounts  ranging  from  0.5  per 
cent  to  occasionally  5  per  cent  or  more  in  some  poor  coals.  It  is 
contained  in  them  usually  as  iron  pyrites  (sulphide  of  iron),  but  some- 
times as  sulphate  of  lime.  It  is  always  on  objectionable  constituent 
of  coal,  since  it  causes  the  formation  of  clinker  by  the  fusion  of  the 
ash.  It  has  a  slight  value  as  fuel  when  in  the  form  of  sulphide  of 
iron,  1  Ib.  of  sulphur  in  that  form  having  a  heating  value  about  equal 
to  that  of  J  Ib.  of  carbon.  In  the  form  of  sulphate  of  lime  it  has  no- 
heating  value. 


18 


STEAM-BOILER  ECONOMY. 


Properties  of  Air. — Pure  dry  air  is  composed  of  a  mixture  of 

20.91  parts  0  and  79.09  parts  N  by  volume, 
or    23.15  parts  0  and  76.85  parts  N  by  weight. 

The  figure  20.91  is  the  average  result  of  several  determinations  of 
oxygen  in  air,  given  in  Hempel's  Gas  Analysis.  The  parts  by 
weight  are  calculated  from  this  figure,  using  15.963  and  14.012  as 
the  relative  density,  respectively,  of  oxygen  and  nitrogen,  referred  to 
hydrogen  as  1. 

The  proportions  usually  given  in  text-books  are:  by  volume,  21  0, 
79  N;  and  by  weight,  23  0,  77  N. 

The  proportion  of  nitrogen  to  oxygen  by  weight  is  76.85  -r-  23.15 
=  3.320;  by  volume,  79.09  -f-  20.91  =  3.782. 

The  proportion  of  air  to  oxygen  by  weight  is  100  -=-  23.15  =  4.320; 
by  volume,  100  -4-  20.91  =  4.782. 

Ordinary  atmospheric  air,  outdoors,  contains  about  4  parts  in 
10,000  of  carbon  dioxide,  and  a  quantity  of  vapor  of  water  depending 
upon  the  temperature  and  the  relative  humidity  of  the  atmosphere. 
The  relative  humidity  is  the  percentage  of  moisture  contained  in  the 
air  as  compared  with  the  amount  it  is  capable  of  holding  at  the  same 
temperature;  it  is  determined  by  the  use  of  the  dry-  and  wet- bulb 
thermometer.  The  degree  of  saturation  for  different  readings  of  the 
thermometer  is  given  in  the  following  table,  condensed  from  one  pub- 
lished by  the  U.  S.  Weather  Bureau  in  1897: 

RELATIVE  HUMIDITY,  PER  CENT. 


s-T 

£ 
0 

I* 

!si 
jl 

Q 

Difference  between  the  Dry  and  Wet  Thermometers,  Deg.  F. 

1 

8 

3 

4 

5 

8 

7 

B 

9 

10 

11 

12 

i:i 

14 

15 

16 

17 

18 

if 

•20 

X,l 

2-, 

22 

24 

2C 

28 

80 

Relative  Humidity,  Saturation  being  100. 

32 
40 
50 
60 
70 
80 
90 
100 
110 
120 
140 

90 
92 
93 
94 
95 
96 
96 
97 
97 
97 
97 

79 
84 
87 
89 
90 
92 
92 
93 
94 
94 
95 

69 
76 

80 
84 
86 
87 
88 
90 
90 
91 
92 

59 

68 
74 
78 
81 
83 
85 
86 
87 
88 
89 

50 

60 
67 
73 

77 
79 
81 
83 
84 
85 
87 

40 
53 

61 
68 

72 
75 
78 
80 
81 
83 
84 

31 
45 
55 
63 

68 
72 
75 
77 
78 
80 
82 

21 

38 
50 
58 
64 
6* 
71 
74 
76 
77 
79 

12 
30 
44 
53 
60 
64 
(58 
71 
73 
75 
77 

3 
22 

38 
48 
55 
61 
65 
68 
70 
72 
75 

16 
33 
44 
52 
57 
62 
65 
67 
70 
73 

8 
27 
39 
48 
54 
59 
(52 
65 
67 
71 

1 

22 
34 
44 
51 
56 
59 
62 
65 
68 

16 
30 
40 
47 
53 
57 
60 
62 
66 

11 
26 
3(5 
44 
50 
54 
57 
60 
64 

6 
22 
33 
41 
47 
51 
55 
58 
62 

1 
18 
29 
38 
44 
49 
53 
56 
60 

14 
26 
35 
41 
47 
50 
54 
58 

10 
23 
32 
39 

44 
48 
51 
56 

6 

19 
29 
36 
42 
46 
49 
55 

2 
16 
26 
34 
39 
44 
47 
53 

13 

23 
32 
37 

42 
45 
51 

10 
20 
29 
35 
40 
44 
49 

7 
18 
26 

33 

38 
42 

48 

1 

13 
22 
29 
34 

38 
44 

8 
17 
25 
30 
35 
41 

3 

13 
21 

27 
31 
38 

FUEL  AND   COMBUSTION. 


19 


WEIGHTS  OF  AIR,  VArOR  OF  WATER,  AND  SATURATED  MIXTURES  OF  AIR  AND 
VAPOR  AT  DIFFERENT  TEMPERATURES,  UNDER  THE  ORDINARY  ATMOSPHERIC 
PRESSURE  OF  29.921  INCHES  OF  MERCURY. 


a 

g 

Mixtures  of  Air  Saturated  with  Vapor. 

j£  - 

a  . 

.2  !SJi 

ci  >, 

**  5 

Elastic 

Weight  of  Cnbic  Foot  of  the 

flf 

s-i->  <£ 

o  2 

Force  of 

Mixture  of  Air  and  Vapor. 

Weight 

^s  *  3 

§g 

the  Air  in 

of 

2  "3 

<k-  '""   ~C3 

C«w 

Mixture 

Vapor 

[1 

III 

fc  ° 

O  cS 

of  Air  and 
Vapor, 
Inches  of 
Mercury. 

Weight 
of  the  Air. 
Ibs. 

Weight 
of  the 
Vapor, 
pounds. 

Total 
Weight  of 
Mixture, 
pounds. 

mixed 
with  1  lb. 
of  Air, 
pounds. 

0° 

.0864 

.044 

29.877 

.0863 

.000079 

.086379 

.00092 

12 

.0842 

.074 

29.849 

.0840 

.000130 

.084130 

.00155 

22 

.0824 

.118 

29.803 

.0821 

.000202 

.082302 

.00245 

32 

.0807 

.181 

29.740 

.0802 

.000304 

.080504 

.00379 

42 

.0791 

.267 

29.654 

.0784 

.000440 

.078840 

.00561 

52 

.0776 

.388 

29.533 

.0766 

.000627 

.077227 

.00819 

62 

.0761 

.556 

29.365 

.0747 

.000881 

.075581 

.01179 

72 

.0747 

.785 

29.136 

.0727 

.001221 

.073921 

.01680 

82 

.0733 

1.092 

28.829 

.0706 

.001667 

.072267 

.02361 

92 

.0720 

1.501 

"    28.420 

.0684 

.002250 

.070717 

.03289 

102 

.0707 

2.036 

27.885 

.0659 

.002997 

.068897 

.04547 

112 

.0694 

2.731 

27.190 

.0631 

.003946 

.067046 

.06253 

122 

.0682 

3.621 

26.300 

.0599 

.005142 

.065042 

.08584 

132 

.0671 

4.752 

25.169 

.0564 

.006639 

.063039 

.11771 

142 

.0660 

6.165 

23.756 

.0524 

.008473 

.060873 

.16170 

152 

.0649 

7.930 

21.991 

.0477 

.010716 

.058416 

.22465 

162 

.0638 

10.099 

19.822 

.0423 

.013415 

.055715 

.31713 

172 

.0628 

12.758 

17.163 

.0360 

.016682 

.052682 

.46338 

182 

.0618 

15.960 

13.961 

.0288 

.020536 

.049336 

.71300 

192 

.0609 

19.828 

10.093 

.0205 

.025142 

.045642 

1.22643 

202 

.0600 

24.450 

5.471 

.0109 

.030545 

.041445 

2.80230 

212 

.0591 

29.921 

0.000 

.0000 

.036820 

.036820 

Infinite. 

The  weight  in  Ibs.  of  the  vapor  mixed  with  100  Ibs.  of  pure  air  at  any  given 
temperature  and  pressure  is  given  by  the  formula 

62,3  X  #29.92 


29.92  -  E 


P 


where  E  =  elastic  force  of  the  vapor  at  the  given  temperature,  in  inches  of  mer- 
cury; p  =  absolute  pressure  in  inches  of  mercury,  =  29.92  for  ordinary  atmos- 
pheric pressure. 

OXYGEN   AND  AIR  REQUIRED  FOR   THE   COMBUSTION  OF  CARBON,  HYDROGEN,  ETC. 

Chemical  Reaction. 

Carbon  to  CO2   C  +  2O  =  CO2 

Carbon  to  CO C  -f  O  =  CO 

Carbon  monoxide  to  C02 CO  +  O  =  CO 

Hydrogen  to  H2O  H  -f  O  =  H2O 

CH4+20=C03+2H20 


Sulphur  to  SO2. S02-j-S-f20  =  S02 


Lbs.  O 
per  lb. 
fuel. 

Lbs.  N  = 
3.32  xO. 

Air  per 
lb.  = 
4.32xO. 

Gaseous 
product 
per  bl. 

e*cHK**|t- 
<M  TH  00 

8.85 
4.43 
l.ftO 
26.56 

11.52 
5.76 
2.47 
34.56 

12.53 
6.76 
3.47 
35.56 

>    4 

13.28 

17.28 

18.38 

1 

3.33 

4.32 

5.33 

20 


STEAM-BOILER  ECONOMY. 


Name. 


Symbol. 


DENSITIES 

OF   GASES. 

Specific 
Gravity. 
Air  =  1. 

Wt.  of 
1  litre. 
Grams. 

1.10521 

1.43003 

0.9701 

1.25523 

0.069234 

0.089582 

1.51968 

1.96633 

0.96709 

1.25133 

0.55297 

0.71549 

0.96744 

1.25178 

0.89820 

1.16219 

2.21295 

2.86336 

1 

1.2939   - 

Wt.  of 

1  on.  ft. 

Lb. 

0.88843 
0.78314 
0.05589 
1.22681 
0.78071 
0.44640 
0.78100 
0.73010 
1.78646 
.080728 


Relative    Do.,  ap- 
Density.   proximate 
figures. 

:      16 


H  = 
15.96 
14.01 

1 

21.95 
13.97 

7.99 
13.97 
12.97 
31.96 


14 
1 

22 
14 
8 
14 
13 
32 


Oxygen O 

Nitrogen N 

Hydrogen H 

Carbon  dioxide CO2 

Carbon  monoxide. . . .     CO 

Methane CH4 

Ethylene C2H4 

Acetylene C2H2 

Sulphur  dioxide S02 

Air 

The  first  two  columns  of  figures  are  from  Hempel's  Gas  Analysis,  credited 
therein  to  Landolt  and  Bernstein's  Pliysikaliscli-chemische  Tabellen.  The  litre 
weights  are  referred  to  Berlin.  The  weights  per  cubic  foot  are  based  on  the 
weight  of  air  given  by  Rankine,  0.080728  Ib.  per  cu.  ft.  at  32°  F.  and  atmospheric 
pressure,  and  the  figures  in  the  column  of  specific  gravities. 

Heating  Values  of  Various  Substances. — The  following  table  gives 
the  heating  values  of  different  pure  fuels,  as  determined  By  burning 
them  in  oxygen  in  a  calorimeter: 

HEAT  OF  COMBUSTION   OF  VARIOUS  SUBSTANCES  IN  OXYGEN. 


Heat-units. 
Cent. 


(  34  46? 
Hydrogen  to  liquid  water -j  g^'g^g 

Carbon  (wood  charcoal)  to  carbon]  8,080 

dioxide,  C02 \  8,137 

Carbon,  diamond  to  CO2 7,859 

"        black  diamond  to  C02 7,861 

"  graphite  to  CO2 7,901 

Carbon  to  carbon  monoxide,  CO.. . .  2,473 

CO  to  CO2,  per  unit  of  CO j    g'gg? 

O  to  C02  per  unit  of  C,  =  2£  X  2403  s',607 
Methane  (marsh-gas),  CH4  to  CO2  (13,120 

andH20 1 13,063 

Ethylene  (olefiant  gas),  C2H4  to  C02  (  11,858 

andH20    1  11,957 

Benzole  gas,  C«H6  to  CO2  and  H2O.  j   9^5 

Acetylene  C2H2 . . . , 10,109 

Sulphur 2,250 

The  heating  value  of  methane,  CH4 ,  if  calculated  according  to  its  composition 
by  the  formula  8080C  -f-  34,463H,  using  Favre  and  Silbermann's  figures,  is 
26,416  Centigrade  heat-units,  instead  of  23,513,  the  value  determined  by  a  calorim- 
eter, a  difference  of  2903  heat-units.  The  calculated  heating  value  of  ethylene, 
C2H4,  is  11,849,  and  that  of  benzole  gas,  C«H6,  is  10,109  heat-units,  differing 
respectively  from  the  calorimetric  values  only  9  and  7  heat-units. 


Fahr. 
62,032 
61,816 
14,544 
14,647 
14,146 
14,150 
14,222 
4,451 
4,325 
4,293 
10,093 
23,616 
23,513 
21,344 
21,523 
18,184 
17,847 
18,196 
4,050 


Authority. 

Favre  and  Silbermann. 

Thomsen. 

Favre  and  Silbermann. 

Berthelot. 


Favre  and  Silbermann* 
it 

Thomsen. 

Favre  and  Silbermann. 

Thomsen. 

Favre  and  Silbermann. 
ii 

Thomsen. 

Favre  and  Silbermann. 

Calculated. 

N.  W.  Lord.* 


*  See  Appendix  to  this  chapter,  Heating  Value  of  Sulphur  in  Coal,  p.  35. 


FUEL  AND   COMBUSTION.  21 

In  calculations  of  the  heating  value  of  mixed  fuels  the  value  for 
carbon  is  commonly  taken  at  14,600  British  thermal  units,  which  is 
approximately  the  average  of  the  figures  given  by  Favre  and  Silber- 
mann  and  by  Berthelot,  and  that  of  hydrogen  at  62,000,  which  is 
nearly  the  average  of  the  figures  of  Favre  and  Silbermann  and  of 
Thomson. 

Taking  the  heating  value  of  C  burned  to  C02  at  14,600  B.T.U., 
and  that  of  C  to  CO  at  4450,  the  difference,  10,150  B.T.U.,  is  the  heat 
lost  by  the  imperfect  combustion  of  each  pound  of  carbon  burned  to 
CO  instead  of  C02.  If  the  CO  formed  by  this  imperfect  combustion 
is  afterwards  burned  to  C02,  the  lost  heat  is  regained. 

Heat  Absorbed  by  Decomposition, — By  the  decomposition  of  a 
chemical  compound  as  much  heat  is  absorbed  or  rendered  latent  as 
was  evolved  when  the  compound  was  formed.  •  If  1  Ib.  C.  is  burned  to 
C02,  generating  14,600  B.T.U.,  and  the  C02  thus  formed  is  immedi- 
ately reduced  to  CO  by  passing  it  through  a  body  of  glowing  carbon, 
.by  the  reaction  C02  +  C  =  2 CO,  the  result  is  the  same  as  if  the 
2  Ibs.  C.  had  been  originally  burned  to  2CO,  generating  2  X  4450  = 
8900  B.T.U.  The  2  Ibs.  C.  burned  to  C02  would  generate  2  X  14,600  = 
29,200  B.T.U.,  the  difference,  29,200  —  8900  =  20,300  B.T.U.,  being 
absorbed  or  rendered  latent  in  the  2CO,  or  10,150  B.T.U.  for  each 
pound  of  carbon. 

In  like  manner  if  9  Ibs.  of  water  (which  might  be  formed  by  burn- 
ing 1  Ib.  H  with  the  generation  of  62,000  B.T.U.  and  cooling  the 
resulting  H20  to  the  atmospheric  temperature)  be  injected  into  a  large 
bed  of  glowing  coal,  it  will  be  decomposed  into  1  Ib.  H  and  8  Ibs.  0. 
The  decomposition  will  absorb  62,000  B.T.U.,  cooling  the  bed  of  coal 
this  amount,  and  the  same  quantity  of  heat  will  again  be  evolved  if 
the  H  is  subsequently  burned  with  a  fresh  supply  of  0.  The  8  Ibs.  0 
will  enter  into  combination  with  6  Ibs.  C,  forming  14  Ibs.  CO  (since  CO 
is  composed  of  12  parts  C  to  16  parts  0),  generating  6x4450  = 
26,700  B.T.U.,  and  6x10,150  =  60,900  B.T.U.  will  be  latent  in  this 
14  Ibs.  CO,  to  be  evolved  later  if  it  is  burned  to  C02  with  an  additional 
supply  of  8  Ibs.  0. 

Heating  Value  of  Compound  or  Mixed  Fuels. — It  is  customary  to 
consider  the  heating  value  of  a  compound  or  mixed  fuel  as  being  equal 
to  the  sum  of  the  heating  values  of  its  elementary  constituents,  and 
to  calculate  it  by  means  of  Dulong's  formula,  which  is,  using  approxi- 
mate figures, in  British  thermal  units, 

Heating  value  =  -^("14,6000  +  62,00of  II  -  -}+  4050S1 ; 
1UU[__  \  »/ 


22  STEAM-BOILER  ECONOMY. 

or,     Heating  value  =  -L[~8140C  +  34,400^H  -  §)  +  2250£~] 

in  Centigrade  units,  in  which  C,  H,  0,  and  S  are  respectively  the  per- 
centages 'of  carbon,  hydrogen,  oxygen,  and  sulphur  contained  in  the 
fuel.  The  term  H  —  £0  is  called  the  ''available  "  or  "  disposable  " 
hydrogen,  or  that  which  is  combined  with  oxygen  in  the  fuel. 

This  formula  does  not  apply  in  the  case  of  a  mixed  gaseous  fuel 
containing  carbon  monoxide,  since,  as  shown  in  the  table  given  above, 
1  Ib.  C  in  the  form  of  CO  generates  when  burning  to  C02  only 
10,093  B.T.U.  instead  of  14,544  B.T.TJ.  (Favre  and  Silbermann's 
values),  the  difference,  4451  B.T.U.,  having  already  been  generated 
when  the  CO  was  formed.  The  formula  also  does  not  appear  to  hold 
true  in  the  case  of  some  hydrocarbon  gaseous  fuels,  as  in  the  case  of 
methane,  mentioned  in  the  note  under  the  table,  while  on  the  other 
hand  it  does  appear  to  hold  in  the  case  of  ethylene  and  benzole. 

For  all  the  common  varieties  of  coal,  cannel-coal  and  some  lignites 
being  excepted,  it  is  accurate  within  the  limits  of  error  of  chemical 
analyses  and  calorimetric  determinations,  as  is  shown  by  the  recent 
experiments  of  Mahler  and  of  Lord  and  Haas,  which  are  discussed 
elsewhere  in  this  volume. 

"Available  Heating  Value  "  of  Hydrogen. — Some  writers  in  giving 
the  heating  value  of  hydrogen  subtract  from  its  total  calorimetric 
value,  62.000  B.T.U.  (found  by  burning  the  gas  in  a  calorimeter  in 
which  the  steam  generated  by  the  combustion  is  condensed  and  cooled 
to  the  temperature  of  the  water  in  the  calorimeter),  a  quantity  rep- 
resenting the  latent  heat  of  the  steam  generated,  viz.,  965.7  B.T.TJ. 
per  Ib.  steam,  or  9  X  965.7  =  8691.3  B.T.U.  per  Ib.  hydrogen,  making 
the  net  heating  value  of  hydrogen  "  burned  to  steam  at  212°  "  62,000  - 
8691  =  53,309  B.T.U.  per  Ib.  Others  subtract  also  an  additional 
quantity  representing  the  difference  between  the  heat  in  the  9  Ibs.  of 
water  condensed  from  the  steam  at  212°  and  that  in  the  same  water 
when  cooled  down  to  a  given  standard  temperature,  such  as  62°.  This 
difference  is  150.9  B.T.U.  per.  Ib.  water,  or9  X  150.9  =  1353.1  B.T.U. 
per  Ib.  hydrogen,  which  subtracted  from  53,309  gives  51,951  B.T.U. 
as  the  available  heating  value  of  1  Ib.  hydrogen  burned  with  8  Ibs. 
oxygen,  both  gases  being  supplied  at  62°,  and  the  product,  9  Ibs.  H20, 
escaping  as  steam  at  212°. 

This  use  of  heating  values  of  hydrogen  "  burned  to  steam,"  in 
computations  relating  to  combustion  of  fuel,  is  inconvenient,  since  it 


FUEL  AND   COMBUSTION.  23 

necessitates  a  statement  of  the  conditions  upon  which  the  figures  are 
based;  and  it  is,  moreover,  misleading,  if  not  inaccurate,  since  hy- 
drogen in  fuel  is  not  often  burned  in  pure  oxygen,  but  in  air,  the 
temperature  of  the  gases  before  burning  is  not  often  the  assumed 
standard  temperature,  and  the  products  of  combustion  are  rarely  dis- 
charged at  212°.  In  steam-boiler  practice  the  chimney-gases  are 
usually  discharged  at  a  temperature  above  300°;  but  if  economizers 
are  used,  and  the  water  supplied  to  them  is  cold,  the  gases  may  be 
cooled  to  below  212°,  in  which  case  the  steam  in  the  gases  is  condensed 
and  its  latent  heat  of  evaporation  is  utilized. 

If  there  is  any  need  at  all  of  using  figures  of  the  "  available  "  heat- 
ing value  of  hydrogen,  or  of  its  heating  value  when  "burned  to  steam/' 
the  fact  that  the  gas  is  burned  in  air  and  not  in  pure  oxygen  should 
be  taken  into  consideration.  The  resulting  figures  will  then  be  much 
lower  than  those  above  given,  and  they  will  vary  with  different  con- 
ditions, as  shown  below. 

(1)  Suppose  1  Ib.  H  to  be  burned  in  just  enough  air  to  supply  8 
Ibs.  0,  that  the  H  and  the  air  are  supplied  at  62°,  and  the  products 
of  combustion  escape  at  212°.     We  have: 

Total  heating  value  of  1  Ib.  H 62,000  B.T.U. 

Heat  lost,  latent  heat  of  9  Ibs.  H2O  at  212°.. . .  =  8691 

9  Ibs.  H20  heated  from  62°  to  212° =  1358 

Nitrogen  with  8  Ibs.  O  heated  from  62C  to  212° 

=  8  X  3.32  X  150  X  0.2438  (specific  heat)  =     971     11,020       " 

Net  available  heating  value 50,980       " 

(2)  Suppose  that  the  air-supply  is  double  that  required  to  effect 
the  combustion  of  the  H,  other  conditions  being  the  same  as  in  (1). 
The  additional  heat  lost  will  be: 

Excess  air  8  X  4.32  =  34.56  Ibs.  X  150  X  0.2375 =     1,231  B.T.U. 

Which  will  reduce  the  net  heating  value  to 49,749       " 

(3)  Suppose  that  with  the  double  air-supply  the  products  of  com- 
bustion escape  at  562°.     The  heat  lost  will  then  be  as  below: 

9  Ibs.  water  heated  from  62°  to  212° 1,358  B.T.U. 

Latent  heat  of  9  Ibs.  H2O  at  212° 8,691       «« 

Superheated  steam,  9  Ibs.  X  (562  -  212)  X  0.48  (sp.  ht.)  1,512       " 

Nitrogen,  26.56  X  (562  -  62)  X  0.2438 3,238       " 

Excess  air,  34.56  X  (562  -  62)  X  0.2375 4,104       •«' 

Total  losses 18,902      " 

Which  subtracted  from  62,000  gives  41,098  B.T.U.  as  the  net  avail- 
able heating  value. 


24:  STEAM-BOILER  ECONOMY. 

It  is  better  in  all  calculations  of  the  heating  value  of  fuel,  and  of 
the  results  of  combustion  in  steam-boiler  practice,  to  avoid  the  use  of 
this  so-called  "available  heating  value/'  and  to  take  the  heating  value 
of  hydrogen  (or  that  part  of  the  hydrogen  which  is  not  already  com- 
bined with  oxygen  in  the  fuel)  at  62,000  B.T.U.  The  various  heat 
losses,  calculated  as  above,  which  vary  with  the  conditions,  are  then 
not  subtracted  from  the  heating  value  of  the  fuel,  but  are  taken  as 
losses  of  heat  in  the  chimney-gases. 

In  calculations  of  the  relative  commercial  value  of  different  fuels 
containing  hydrogen  or  water,  however,  account  must  be  taken  of  the 
loss  of  heat  due  to  superheated  steam  escaping  in  the  chimney-gases. 

Available  Heating  Value  of  a  Fuel  containing  Hydrogen. — The 
total  heating  value  of  a  hydrogenous  fuel  being 


14,6000  +  62,000(H  -  2\, 
\  o/ 


to  find  the  available  heating  value  for  any  assumed  temperature  of  the 
air-supply  and  of  the  chimney-gases,  we  subtract  the  heat  lost  in  the 
superheated  steam  which  escapes  into  the  chimney,  or 


9H  X  [(212°.9  -  0  +  965-7  +  0.48(7;  -  212°)], 

in  which  t  is  the  temperature  of  the  air-supply  and  Tf  that  of  the 
chimney-gases.  This  calculation  takes  no  account  of  the  nitrogen 
which  is  in  the  air  required  to  burn  the  hydrogen,  nor  of  the  excess 
air-supply,  the  loss  of  heat  due  to  these  being  considered  as  part  of  the 
loss  in  the  dry  chimney-gases,  consisting  of  C02  ,  CO,  0,  and  N.  (The 
figures  212.9  and  965.7  are  usually  taken  as  212  and  966  with  suffi- 
cient accuracy.) 

EXAMPLE.  —  What  is  the  total  heating  value  and  the  available  heat- 
ing value  of  1  Ib.  of  combustible  consisting  of  0.91C  +  .05H  -j-  .040, 
the  air  for  combustion  being  supplied  at  62°  and  the  chimney-gases 
escaping  at  562°  ? 

Total  beating  value,  0.91  X  14,600+  .045  X  62,000  ............  =  16,076  B.T.U. 

Heat  lost  in  steam,  9  X  .05[150  +  966  +  (0,48  X  850)]  ..........  =       578       " 

Difference,  or  available  beating  value  .....................  15,498       " 

The  heat  lost  in  the  steam  is  about  3.5$  of  the  total  heating  value. 

Available   Heating  Value  of  a   Fuel  containing  Hydrogen  and 

Water.  —  In  this  case  the  heat  lost  includes,  besides  that  due  to  the 


FUEL  AND   COMBUSTION.  25 

superheated  steam  formed  by  the  combustion  of  the  available  hydro- 
gen, that  is,  the  hydrogen  of  the  dry  fuel  less  one-eighth  of  the  oxygen 
of  the  dry  fuel,  the  heat  due  to  the  superheated  steam  formed  from 
the  water  in  the  fuel,  or 

(9H  -f  W)  X  [(212  -t)  +  966  +  0.48(7;  -  212)], 

in  which  W  is  the  water  in  1  Ib.  of  the  fuel. 

EXAMPLE. — What  is  the  available  heating  value  of  1  Ib.  of  moist 
wood  whose  analysis  is  380,  511,  320,  1  ash,  24  water,  =  100$,  the 
air  being  supplied  at  62°  F.  and  the  chimney-gas  escaping  at  412°  ? 

Total  heating  value,  38  X  14,600+  (5  -  4)  X  62,000 =  6168  B.T.U. 

Heat  lost  in  superheated  steam,  (9  X  .05  +  0.24) 

X  [150  +  966  +  (0.48  X  200)] =    836      " 

Available  heating  value =  5332      " 

The  heat  lost  in  the  steam  in  this  case  is  nearly  14$  of  the  total 
heating  value. 

Temperature  of  the  Fire, — Assuming  that  a  pure  fuel,  such  as 
carbon,  is  thoroughly  burned  in  a  furnace,  all  of  the  heat  generated 
will  be  transferred  to  the  gaseous  products  of  combustion,  raising  their 
temperature  above  that  at  which  the  fuel  and  the  oxygen  or  air  are 
supplied  to  the  furnace.  Suppose  that  1  Ib.  0  is  burned  with  2f  Ibs. 
0,  forming  3§  Ibs.  C0a,  both  the  0  and  the  0  being  supplied  at  0°F. 
The  combustion  of  the  1  Ib.  0  generates  14,600  B.T.U. ,  which  will 
all  be  contained  in  the  3f  Ibs.  C02.  The  specific  heat  of  C02  is  0.217; 
that  is,  it  requires  0.217  B.T.U.  to  raise  the  temperature  of  C02  one 
degree  Fahrenheit.  To  raise  3|  Ibs.  C02  one  degree  will  require 
3f  X  0.217  =  0.7957  B.T.U.,  and  14,600  B.T.U.  will  therefore  raise 
its  temperature  14,600  -f-  0.7957  =  18,350°  F.  above  the  temperature 
at  which  the  0  and  the  0  were  supplied.  The  temperatures  thus 
calculated  are  known  as  theoretical  temperatures,  and  are  based  on 
the  assumptions  of  perfect  combustion  and  no  loss  by  radiation.  The 
temperature  of  18,350°  is  far  beyond  any  temperature  known  in  the 
arts,  and  it  is  probable  that  long  before  it  could  be  reached  the  phe- 
nomenon of  dissociation  would  take  place;  that  is,  the  C02  would  be 
split  up  into  C  and  0,  and  the  elements  would  lose  their  affinity  for 
each  other. 

The  theoretical  elevation  of  temperature  of  the  fire  may  con- 
veniently be  calculated  by  the  formula 

B.T.U.  generated  by  the  combustion 


Elevation  of  temp.  = 


Weight  of  gaseous  products  x  their  specific  hea'; 


26  STEAM-BOILER  ECONOMY. 

It  is  evident  from  this  formula  that  the  rapidity  of  the  combustion,  or 
the  time  required  to  burn  a  given  weight  of  fuel,  has  nothing  to  do 
with  the  temperature  that  may  theoretically  be  attained.  In  practice 
the  temperature  of  a  bed  of  coal  in  a  furnace  and  that  of  the  burning 
gases  immediately  above  the  coal  are  reduced  to  some  extent  by  radia- 
tion, and  as  the  quantity  of  heat  radiated  from  a  given  mass  of  fuel  is 
a  function  of  the  time  during  which  it  takes  place,  a  considerable  por- 
tion of  the  heat  generated  may  be  lost  by  radiation  when  the  combus- 
tion is  very  slow.  With  ordinary  rates  of  combustion,  however,  say 
10  Ibs.  of  coal  per  sq.  ft.  of  grate  surface  per  hour,  and  fire-brick 
furnaces,  the  percentage  of  loss  of  heat  by  radiation  is  quite  small, 
\</0  or  less,  and  the  actual  temperature  that  may  be  attained  will  be 
very  nearly  as  high  with  that  rate  of  combustion  as  with  a  rate  of  20 
or  40  Ibs. 

Maximum  Theoretical  Temperature  due  to  Burning  Carbon  in  Dry 
Air.— 1  Ib.  0  burned  to  C02  generates  14,600  B.T.U.  The  products 
of  combustion  are  3flbs.  C02  -f  2fx3.32  =  8.853  Ibs.  N  =  12. 52  Ibs. 
gas.  Taking  the  specific  heat  of  C02  at  0.217,  and  that  of  N  at 
0.2438,  we  have  for  the  specific  heat  of  the  gas 

(3|  X  0.217  +  8.853  X  0.2438)  +  12.52  =  0.2359. 

The  elevation  of  temperature  of  the  fire  above  the  atmospheric 
temperature  is  14,600  -J-  12.52  X  0.2359  =  4942.5°. 

If  the  atmospheric  temperature  is  62°  F.,  then  the  temperature  of 
the  fire  is  4956  +  62  =  5004.5.° 

The  temperatures  found  by  the  above  calculations  can  never  be 
reached  in  practice,  since  it  is  not  possible  to  effect  complete  com- 
bustion without  a  considerable  excess  of  air  above  the  theoretical 
requirement.  It  is  also  probable  that  the  specific  heat  of  the  gases  of 
combustion,  at  high  temperatures,  is  higher  than  the  figures  given, 
which  would  have  the  effect  of  reducing  the  temperature. 

Taking  the  specific  heat  of  the  gases  at  0.237,  the  figure  commonly 
taken  in  temperature  calculations,  the  calculated  elevation  of  tempera- 
ture is  14,600  -r-  12.52  x  0.237  =  4920°  F. 

TEMPERATURE  OF  THE  FIRE,  CARBON  BEING  BURNED  PART  TO  CO  AND 

PART  TO  COa. 

Heating  value  of  C  burned  to  CO2 14,600  B.T.U. 

"      "  "       •'       "  CO 4,450       " 

1  Ib.  C  to  C02 ,  with  no  excess  of  air,  gives 12  52  Ibs.  gas. 

lib.  C  to  CO,       "      "       "        "    "        "    6.76    " 


FUEL  AND   COMBUSTION. 


Air-supply  below  11.52  Ibs.,  per  cent.. 

0 
11.52 

10 
10  37 

20 
9  22 

30 

8  06 

40 
6  91 

50 
5  76 

12  52 

11  37 

10  22 

9  06 

7  91 

6  76 

100 

80 

60 

40 

20 

o 

C       "       "CO       "      "    

0 

20 

40 

60 

80 

100 

Heat  generated  in  making  COa  ,  B.T.U. 

14,600 

11,680 

8,760 

5,840 

2 

,920 

0 

"          "        "       CO           " 
Total  heat  generated       .         

0 
14  600 

890 
12  570 

1,780 
10  540 

2,670 
8  510 

3 

,560 

480 

4,450- 
4  450- 

Elevation  of  temperature  of  fire  (tak-  ) 
ing  specific  heat  of  gases  at  0.£4)     f 

4860° 

4606° 

4298° 

3914° 

3 

418° 

2743* 

TEMPERATURE   OF   THE   FIRE,  CARBON   BURNED   TO   CO2    WITH   EXCESS   OF   AIR. 

Air-supply  above  11.52  Ibs.,  per  cent.  25  50  75  100  150  200 

Air  per  Ib.  C,  Ibs 14.40  17.28  20.16  23.04  28.80  34.56 

Air  +  C  =  gas,  Ibs 15.40  18.28  21.16  24.04  29.80  35.56- 

Elevation  of  temperature  of  fire 3950°  3328°  2875°  2530°  2041°  1711* 


J 35- 
"§30- 
^25— 
£20— 


'5000 

4800 

4600 

4400 

4200 

4000 

3800 

3600 

3400 

3200 

3000 

2800, 

2600 

2400 

2200 

2000 

1800 

1600 


above  115!  its  perhfeof  C>rtx 


50 


25 


25 


125 


150 


175 


200 


50  75  100 

Air    Supply. 

FIG.  1.— MAXIMUM  THEORETICAL  TEMPERATURE  OF  THE  FIRE  DUE  TO  BURN- 
ING CARBON  WITH  DIFFERENT  QUANTITIES  OF  AIR. 

(For  the  two  tables   given  above  and  for  the  diagram  plotted  therefrom  the 
author  is  indebted  to  Mr.  H.  T.  De  Puy  of  the  Babcock  &  Wilcox  Co.) 

CARBON   BURNED   PART   TO    CO2    AND   PART   TO   CO   WITH   EXCESS   OF  AIR. 

C  burned  to  C02 ,  per  cent 
C       "        "  CO       " 
Excess  of  air 
Air  -f  C  =  gas,  Ibs. 


r  cent  

.  .      100         80         60          40         20         0 

0           20         40          60         80       100 

ti 

50          40         30          20         10          0 

..     18.28     15.52     12.99     10.67      8:60     6.76 

iture  of  fire... 

3328°    3375°    3350°    3323°    3139°    2743° 

28  STEAM-BOILER  ECONOMY. 

Maximum  Theoretical  Temperature  due  to  Burning  Hydrogen  in 
Dry  Air.—  1  Ib.  H  burned  to  H20  generates  62,000  B.T.TJ.  The 
products  of  combustion  are  9  Ibs.  H20  (superheated  steam)  and 
8X3.32  =  26.56  Ibs.  N.  Let  t  —  temperature  of  the  atmosphere 
and  T-\-  1  =  temperature  of  the  products  of  combustion,  0.48  =  spe- 
cific heat  of  superheated  steam,  and  0.2438  =  specific  heat  of  nitrogen. 
Then 


212.9  is  the  B.T.U.  above  0°  F.  in  1  Ib.  of  water  at  212°,  965.7  is  the 
latent  heat  of  evaporation  at  212°,  and  0.48(T  +  t  —  212)  is  the  heat 
required  to  heat  1  Ib.  of  steam  from  212°  to  the  temperature  T+t. 
Taking  /  at  62°,  we  have 

62,000  =  9  [1044.6  +  0.48  T]  +  6.475I7 

=  9401.4  +  10.  795  T. 
Whence  T  =  4872.5,     and     T+  t  =  4934.5°  F. 

The  term  (212.9  —  /)  is  usually  written  (212  —  t);  the  difference 
is  unimportant,  causing  less  than  1°  F.  error  in  the  result. 

The  maximum  theoretical  temperature  due  to  burning  hydrogen 
in  air  and  that  due  to  burning  carbon  in  air  are  very  nearly  the  same. 
Temperature  of  the  Fire,  the  Fuel  containing  Hydrogen  and 
Water.  —  The  ga'seous  products  of  combustion  in  this  case  will  contain 
superheated  steam,  formed  from  the  combustion  of  the  hydrogen  in 
the  coal  and  the  evaporation  of  the  moisture.  The  calculation  of  the 
temperature  of  the  fire,  assuming  perfect  combustion  and  no  loss  by 
radiation,  may  be  made  in  the  following  manner.  Eeduce  the  analy- 
sis of  the  fuel  in  percentages  of  C,  H,  0,  and  moisture  to  decimal 
parts  of  1  Ib. 

Let  Hl  =  H  —  10  =  available  hydrogen; 
W  =  moisture  in  the  coal  ; 
jf  =  elevation  of  the  temperature  of  the  fire  above  the  atmos- 

pheric temperature; 

t  =  temperature  of  the  atmosphere,  say  60°  'F.; 
L  —  latent  heat  of  evaporation  at  212°  —  966; 
a  =  heating  value  of  1  Ib.  of  carbon  =  14.600; 
b  =      "  "     "    1  Ib.  of  hydrogen  =  62,000; 

/=  Ibs.  of  dry  gas  per  Ib.  of  carbon  =  C02  -j-  N  -j-  excess  air; 
c  =  specific  heat  of  the  gas  =  0.237; 
$H=  Ibs.  of  steam  formed  by  burning  the  available  H  ; 
W-{-  9//—  superheated  steam  in  the  gases; 
0.48  =  specific  heat  of  superheated  steam. 


FUEL  AND   COMBUSTION.  29 

The  total  heat  developed  by  burning  1  Ib.  of  the  fuel  will  be 
aO-\-  bffl  heat-units. 

All  of  this  heat  will  be  utilized  in  raising  the  temperature  of  the 
gas  and  steam  to  T°  above  the  atmosphere.  The  dry  gas  will  contaia 
cfT  heat-units,  and  the  superheated  steam 

(W+  9H)  [212  -  t  +  L  +  0.4S(T  +  t  -  212)]. 
We  have  then 


=  [0.237/  +  QA8(W+9H)]T+(W+  9#)(1077  -  0.52J). 
Transposing, 


_  ac+  IH^  -  (  W+  9^)  (1077  -  0.52Q 
0.237/+0.48(JF+9#) 

Substituting  for  a,  b,  and  H^  their  values,  and  taking  t  =  62°, 
_  14,600(7+  62,000(#-  J0)  -  1044.6(  W  +  9H) 

0.237/4-  0.48(JF+9#) 

Taking  C,  H,  0,  and  W  in  percentages,  instead  of  in  decimal  parts, 
the  formula  reduces  to  (a  very  close  approximation) 

_  616(7+  2220#-  3270  -  44  W 
/+  0.02  PF  +0.18,9" 

EXAMPLES.  —  1.  Given  a  coal  whose  analysis,  excluding  ash  and  sul- 
phur, is  75C,  511,  100,  and  10  moisture,  with  dry  gas  =  20  Ibs.  per 
Ib.  of  this  combustible,  including  moisture  : 

616  X  75  +  2220  X  5  -  327  X  10  -  44  X  10  _  2-     0 
20  +  .02  X  10  +.18  X  5 

T+t  =  2600°  F. 

The  first  of  the  two  formulas  gives  2602°  F. 

The  sulphur  in  coal  may  be  neglected  in  calculations  of  tempera- 
ture, since  3  per  cent  of  sulphur  would  not  increase  the  temperature 
one  per  cent,  taking  4000  B.T.U.  as  the  heating  value  of  sulphur. 
The  error  due  to  neglecting  it  is  less  than  the  probable  error  of  the  fig- 
ure, 0.237,  for  the  specific  heat  of  furnace-gases  at  high  temperatures. 
2.  Required  the  maximum  temperature  attainable  by  burning  moist 
wood  of  the  composition  C,  38;  H,  5;  0,  32;  ash,  1;  moisture,  24; 
the  dry  gas  being  15  Ibs.  per  Ib.  of  wood,  and  the  temperature  of  the 
atmosphere  62°. 

_  616  X  38  +  2220  X  5  -  327  X  32  -  44  X  24       U03o. 
15  _j_  .02  X  24  +  0.18  X  5 
T+  t  =  1465°. 


SO  STEAM-BOILER  ECONOMY. 

3.  Since  the  carbon  and  the  available  hydrogen  make  only  39$  of 
the  weight  of  the  wood,  a  much  smaller  air-supply  than  that  required 
to  make  15  Ibs.  of  dry  gas  per  Ib.  of  wood  may  be  sufficient  to  effect 
-complete  combustion.  If  we  take  the  dry  gas  at  10  Ibs.  instead  of  15, 
the  temperature  T  will  be 

OOQQQ 
_          ~"^< 

- 


10  +  1.38  - 

4.  Required  the  theoretical  temperature  of  a  fire  of  Pocahontas  coal 
of  the  following  analysis:  C,  84.22;  H,  4.26;  0,  3.48;  N,  0.84;  S, 
€.59;  ash,  5.85;  water,  0.76;  the  dry  gas  being  20  Ibs.  per  Ib.  of  com- 
bustible, the  heating  value  of  the  S  being  neglected. 

The  combustible,  C,  H,  0,  and  N,  is  92.80$  of  the  coal; 

/=  20  X  .928  =  18.56. 

616  X  84.22  +  2220  X  4.26  -  327  X  3.48  -  44  X  0.76  _  01100. 
18.56  +  .02  X  0.76  +  .18  X  4.26 

T+  t  =  3110  +  62°  =  3172°. 

Pure  carbon  burned  with  19  Ibs.  air  per  Ib.,  making  20  Ibs.  of  gas, 
by  the  same  formula  gives  T—  3080,  T  -\-  1  =  3142.  The  semi-bitumi- 
nous coal  therefore  gives  a  trifle  higher  temperature  than  pure  carbon. 

Actual  Temperature  of  the  Fire  usually  Less  than  the  Theoretical.  — 
In  order  to  realize  in  practice  the  temperatures  given  by  the  above 
theoretical  calculations,  it  is  necessary  that  the  air  be  delivered  to  the 
incandescent  fuel  at  a  perfectly  uniform  rate;  that  the  combustion  of 
the  hydrogen  be  complete  ;  that  the  combustion  of  the  carbon  be  com- 
plete, forming  C02  when  the  air-supply  equals  or  exceeds  11.52  Ibs  per 
Ib.  of  carbon  burned,  or,  when  the  air-supply  is  less  than  this,  that  all 
of  its  oxygen  be  used  to  form  either  CO  or  C02  ;  and  that  there  be  no 
loss  by  radiation  from  the  incandescent  fuel  into  the  surrounding  fur- 
nace or  boiler  walls.  These  conditions  can  be  nearly  obtained  under 
some  circumstances,  such,  for  instance,  as  with  gaseous  fuel  with  an 
intimate  and  regular  admixture  of  air,  the  combustion  taking  place  in 
a  chamber  with  thick  fire-brick  walls  ;  with  dust  fuel  burned  under 
similar  conditions  ;  and  with  a  thick  fire  of  anthracite,  egg  size,  burned 
in  a  fire-brick  chamber  with  a  steady  draft,  after  the  freshly  fired  upper 
layer  of  coal  has  reached  the  temperature  of  the  furnace.  With  insuf- 
ficient air-supply  the  actual  temperature  is  always  less  than  the  theoreti- 
cal, for  the  reason  that  some  of  the  oxygen  passes  through  the  fire 


FUEL  AND   COMBUSTION.  31 

without  entering  into  combination  with  carbon.  Generally  the  air- 
supply  is  not  regular,  even  with  a  steady  draft  pressure,  for  the  reason 
that  the  freshly  fired  coal  chokes  to  some  degree  the  air-passages  through 
the  bed,  causing  the  formation  of  some  CO  and  chilling  the  furnace. 
When  the  fire-bed  is  directly  underneath  the  comparatively  cool  surface 
of  the  boiler,  radiation  from  the  bed  reduces  the  furnace  temperature. 

The  author  has  obtained  temperatures  exceeding  3000°  F.,  as  meas- 
ured by  a  Uehling  &  Steinbart  recording  pneumatic  pyrometer,  with 
Pittsburg  coal  containing  less  than  2$  of  moisture,  and  having  a  heat- 
ing value  of  15,000  B.T.U.  per  Ib.  of  dry  combustible.  The  conditions 
were  a  fire-brick  combustion-chamber  and  frequent  firing  of  small  quan- 
tities of  coal  at  a  time.  This  corresponds  nearly  to  the  theoretical 
temperature  due  to  an  air-supply  of  19  Ibs.  per  Ib.  of  combustible, 
which  is  the  figure  found  in  practice  to  give  the  highest  efficiency  of 
steam-boiler  performance. 

Excessive  Carbon  Monoxide  produced  by  Heavy  Firing. — A  series 
of  experiments  by  J.  C.  Hoadley  (Trans.  A.  S.  M.  E.,  vol.  vi.  p.  794), 
in  which  for  three  hours  anthracite  egg  coal  was  fired  on  the  grates  at 
the  rate  of  200  Ibs.  in  each  half-hour,  when  the  rate  at  which  the  coal 
was  burned  was  only  about  140  Ibs.,  thus  steadily  increasing  the  thick- 
ness of  the  bed  of  coal,  showed  the  following  results,  the  gases  being 
analyzed  every  half-hour: 

Half- liour  periods 1          2          34          5  6*        7*        8 

CO  in  gases,  per  cent..     2.54    2.99     3.99    461  4.70  4.81     0.25    0.21 

C02"       "       "      "...     5.12    5.55    7.79    7.70  7.82  8.0115.2114.11 

Lbs.  air  per  Ib.  coal....     33.2    29.5    21.4    20.1  19.8  19.3     19.3    20.8 

*  Intervals  of  one  hour. 

The  firing  was  at  the  rate  of  200  Ibs.  of  coal  every  half-hour  until 
11.15  A.M.,  or  fifteen  minutes  before  the  sixth  sample  of  gas  was 
taken.  The  next  lot  of  200  Ibs.  coal  was  not  fired  until  12.45  P.M., 
and  no  more  was  fired  until  after  the  eighth  sample  of  gas  was  taken. 
The  seventh  sample  was  taken  at  12.30,  and  the  eighth  at  1.30,  each 
forty-five  minutes  after  firing  200  Ibs.  of  coal.  The  results  show  a 
steady  increase  in  CO  up  to  11.30  A.M.,  as  the  bed  of  coal  became 
thicker,  and  a  reduction  to  a  low  figure  when  the  bed  became  thin.' 

These  tests  show  that  it  is  sometimes  possible  for  a  high  percentage 
of  CO  and  a  great  excess  of  air-supply  to  exist  at  the  same  time.  This 
may  be  explained  by  supposing  that  the  excess  of  CO  was  generated  at 
one  portion  of  the  grate  surface,  and  that  the  excess  of  air  entered  at 
another — or  else  leaked  into  the  boiler-setting  beyond  the  bridge- 
wall — and  that  the  two  currents,  one  of  CO  and  the  other  of  air,  were 


32  STEAM-BOILER  ECONOMY. 

never  brought  into  contact  until  their  temperature  was  reduced  below 
the  point  of  ignition. 

Calculation  of  the  Weight  of  Air  supplied,  and  the  Weight  of  the 
Gases,  from  the  Analysis  of  the  Gases  by  Volume,* — Given  a  coal  con- 
taining 660,  5H,  80,  IN,  8  water,  and  12  ash,  =  100$,  it  is  required 
to  compute  the  analysis,  by  weight  and  by  volume,  of  the  gaseous 
products  of  combustion,  on  the  assumptions  (1)  that  600  is  burnt 
to  C02  and  6  to  00;  (2)  that  the  supply  of  dry  air  is  20$  in  excess  of 
that  required  to  effect  this  combustion  of  the  0  and  to  burn  the  avail- 
able H  (  =  H  —  -§0)  to  H20  ;  and  (3)  that  the  dry  air  is  accompanied 
by  \%  of  its  weight  of  moisture.  It  is  also  required  to  determine  the 
weight  of  dry  air  and  of  dry  gas  per  Ib.  of  carbon  and  per  Ib.  of  fuel, 
and  furthermore  to  find  formulas  by  means  of  which  these  weights 
may  be  computed  directly  from  the  analysis  of  the  gases  by  volume. 

We  first  construct  a  table  in  which  are  shown  the  elements  of  the 
coal  and  of  the  air  which  combine  to  form  the  gaseous  products,  as 
follows : 

Per  cent  or  parts  O  from     N  from  the        Total         rr.          rr.         TT  ^ 

in  100  Ibs.  fuel.  the  air.  air  =  O  X  3.32.        air.  C°2'        CO>        H2°- 

60CtoCO,x2£        =         160        531.20        691.20        220 
6C  to  CO    X  li        =            8          26.56          34.56        ...        14         .. 
4HtoH2Ox8          =          32        106.24        138.24        36 

200        664.00        864.00 

8o[toH'° 9 

IN 1.00 

8  water > 8 

12  ash 

100 

Excess  air,  20$ 40        132.80        172.80 

Total  dry  air 1036 . 80 

Moisture  in  the  air , . .  1 . 04 

Total  gases,  1125.84      =        40         797.8          220  14      54.04 

Total  dry  gases,  1071.80,  or      3.732    74.436     20.526      1.306$  by  wt. 

"       ""       "    %  by  vol.  3.547    80.847     14.187      1.419 

Total  gas  1125.84  +  12  ash  =  100  coal  -f  1036.80  air  +  1.04  moisture  in  air 

Dry  gas  per  Ib.  coal  10.718  Ibs. ;  per  Ib.  C  =  1071 . 8  ~  66  =  16 . 239  Ibs. 

Dry  air  per  Ib.  coal  10.368  Ibs.;  per  Ib.  C  —  1036.8  -%-  66  =  15.709  Ibs. 

*To  convert  analysis  by  volume  into  analysis  by  weight,  multiply  the  per- 
centage of  each  constituent  gas  by  its  relative  density,  viz.,  C02  by  11,  O  by  8, 
CO  and  N  each  by  7,  and  divide  each  product  by  the  sum  of  the  products.  Per 
contra,  to  convert  analysis  by  weight  into  analysis  by  volume,  divide  the  per- 
centage by  weight  of  each  gas  by  its  relative  density,  and  divide  each  quotient  by 
the  sum  of  the  quotients. 


FUEL  AND   COMBUSTION.  33 

The  air  and  gas  per  Ib.  coal  and  per  Ib.  C  may  be  calculated  from 
the  analysis  of  the  gases  by  weight  or  by  volume,  as  follows : 

Let  C02+0-|-CO  +  N=  total  gas,  in  percentages,  by  weight. 
The  carbon  in  the  C02  =  T3TC02,  and  that  in  the  CO  =  -fCO.  This 
carbon  was  supplied  by  the  fuel.  We  then  have 

C02  +  0  +  CO  +  N  100 

Dry  gas  per  Ib.  C  ^  +  ^  ^  +  sCQ  • 

Multiplying  the  result  by  the  C  in  1  Ib.  coal  gives  the  dry  gas  per  Ib. 
of  coal. 

Multiplying  each  term  in  this  formula  by  the  respective  figures  for 
relative  density  of  the  several  gases,  viz.,  C02,  11;  O,  8;  CO  and  N,  7, 
we  obtain 

11C02  +  80  +  7(CO  +  N) 
Dry  gas  per  Ib.  C  •    3(C02  +  CO)         ~' 

In  which  C02,  0,  CO,  and  N  are  percentages  by  volume.    Taking  the 
percentages  by  volume  given  in  the  above  table,  we  have 

11  X  14.187  +  8  x  3.547  +  7  X  82.266 
Dry  gas  per  Ib.  C  —^^.^ 

=  16.239  Ibs.,  as  before. 

Dry  gas  per  Ib.  coal  =  16.239  X  .66  =  10.718  Ibs. 

The  7N  in  the  last  formula  represents  the  N  supplied  by  the  air, 
plus  the  relatively  insignificant  amount  of  about  1  part  in  800  furnished 
by  the  coal,  as  shown  in  the  table.  As  the  N  supplied  by  the  air  is 
76.85$,  or  3.32  -4-  432,  of  the  weight  of  the  air,  we  have 


7(N  -  ,*rN)       432  3.032N 

Dry  an-  per  Ib.  C    =  3}^  ^0)  X  m  =  ^  +  CQ, 

in  which  C02,  CO,  and  N  are  percentages  by  volume  of  the  dry  gas. 
This  last  formula  is  a  most  useful  one  for  computing  the  air-supply 
per  Ib.  C  from  the  analysis  of  the  gases  by  volume.     Substituting  the 
percentages  found  in  the  example,  we  have 

3.032  X  80.84?  n 

Dry  air  per  Ib.  C  =  =  15.707  Ib., 


which  is  practically  the  same  as  the  result  obtained  from  the  table. 


*  If  the  coal  did  not  contain  hydrogen,  the  dry  air  per  Ib.  C.  might  be  computed 
from  the  CO  -f-  O  -f  CO,  instead  of  from  the  N,  by  means  of  the  formula 


This  formula  gives  inaccurate  results  when  the  coal  contains  hydrogen,  for  the  O 


34  STEAM-BOILER  ECONOMY. 

Excess  of  Air-supply  above  the  Theoretical  Minimum  Require- 
ment, —  Referring  to  the  table  of  computations  in  the  above  example, 
p.  32,  it  will  be  seen  that  all  the  nitrogen  in  the  gases,  80.847$  by 
volume,  came  from  the  total  air-supply,  except  an  insignificant 
amount  furnished  by  the  coal.  The  oxygen,  3.547$,  all  came  from 
the  excess  air-supply.  This  oxygen  was  accompanied  in  the  excess 
air-supply  with  3.782  times  its  volume  of  nitrogen,  or  3.782x3.547  = 
13.415N.  The  diiference  between  80.847  and  13.415  =  67.432  is 
the  N  of  the  air  theoretically  required  to  burn  the  coal,  and  the  quo- 
tient, 80.847  -r-  67.432  =  1.199,  is  the  ratio  of  the  total  air-supply  to 
that  theoretically  required.  Subtracting  1  from  this  ratio  and  multi- 
plying by  100  gives  19.9$  as  the  calculated  percentage  of  excess  air- 
supply,  a  close  approximation  to  the  20$  originally  assumed  in  com- 
puting the  table.  The  formula  for  computing  the  percentage  of  excess 
of  air-supply  above  that  theoretically  required  then  is: 

/          N  \ 

Per  cent  excess  air  =  100  xf  -^  _  .,  ^89O  —  1)  . 


N 

The  ratio  of  total  air  to  the  theoretical  requirement  is 


=r=  -  , 

JN  —  3.782O 

in  which  N  and  0  are  respectively  the  percentages  of  N  and  0  by 
volume  in  the  dry  gas.* 

of  the  air  required  to  burn  the  hydrogen  to  H20  does  not  appear  in  th'e  analysis  of 
the  dry  gases.     In  the  example  given  in  the  text,  the  result  calculated  by  this. 


formula  would  be  s^e-  *  419=  13  615  lb  ingtead  of  lg  7Q7 


calculated  by  the  correct  formula. 

This  formula  is  derived  as  follows  :    We  have  found 


Dry  gas  per  lb.  C  =  1^+  80  +  700  +  7N 
3(C02  -f  CO) 

in  which  C02  ,  O,  CO,  and  N  are  percentages  by  volume.  The  oxygen  in 
11C02  +  80  +  7CO  =  8COa  +  80  f  4CO.  The  air  corresponding  to  this  oxygen 
=  4.32  times  the  0,  whence 


a,    e,  „  C  =  4.- 


*  Bunte  gives  a  formula,  quoted  by  Donkin,  for  the  ratio  of  air  in  excess  of 

18  9 
that  theoretically  required  for  combustion  as  follows:  Excess  ratio  =  -~  .     Tak- 

CO2 

ing  the  CO2  in  our  example,  14  187$,  this  formula  shows  the  excess  air-supply  to  be 
33.3$  instead  of  20$,  the  correct  figure.  It  is  evident  that  the  CO2  in  the  gases  is 
not  the  proper  datum  from  which  to  compute  the  air-supply,  for  low  CO2  ,  which 
by  the  formula  would  indicate  a  large  air-supply,  may  be  due  to  high  CO,  which. 
Is  caused  by  a  deficient  air-supply. 


FUEL  AND   COMBUSTION.  35 


APPENDIX   TO    CHAPTER   II. 

I.  HEATING  VALUE  OF  SULPHUR  (AS  IRON  PYRITES)  IN  COAL.* 

A  sample  of  Pocahontas  coal  having  a  calorific  value  of  8062 
(calories)  and  containing  0.57  per  cent  of  sulphur  was  mixed  with 
pyrites  in  two  proportions,  nine  of  coal  to  one  of  pyrites,  and  eight  of 
coal  to  two  of  pyrites.  The  coal  and  pyrites  were  separately  reduced 
to  fine  powder  and  then  mixed  by  rubbing  in  a  mortar.  The  mix- 
tures were  then  compressed  into  cylinders  for  combustion  in  the  bomb 
[the  Mahler  calorimeter].  The  pyrites  used  was  a  selected  crystal 
of  FeSa. 

The  results  were  as  follows: 

No.  1 .   Weight  of  coal  mixtures  taken .  0 . 938  gram 

Actual  beat  developed  after  correction  for  wire  burned  as  fuse     7129  units 

To  calculate  the  heat  due  to  the  production  of  nitric  acid  I  sub- 
tracted the  acidity  due  to  the  sulphuric  acid  produced  from  the  total 
acidity  in  the  bomb-washings  and  figured  the  difference  as  nitric  acid. 
Correcting  the  figure  for  heating-power  for  this  gives  7107  units  for 
the  heat  produced  by  burning  the  0.938  gram  of  mixture,  but  this 
mixture  contained  T9¥  coal.  The  heating  value  of  this  coal  (0.9  X 
0.938  x  80(52)  was  0806.  7107  -  G806  =  301,  the  heat  due  to  the 
combustion  of  the  pyrites. 

The  sulphur  was  determined  in  the  liquid  washed  from  the  bomb. 
It  amounted  to  0.0538  gram;  or,  deducting  the  0.0048  in  the  coal 
present,  0.0490  sulphur  burned  as  pyrites  produced  301  units,  which 
is  in  the  proportion  of  6140  units  for  each  unit  of  sulphur  present  as 
iron  pyrites  in  the  coal. 

A  second  experiment  was  conducted  in  precisely  the  same  manner 
on  the  mixture  containing  eight  parts  of  coal  and  two  parts  of  pyrites. 

H.  u. 

Heat  of  combustion  of  0.921  gram  of  the  mixture 6520 

Heat  due  to  coal 6005 

Heat  due  to  pyrites 51 5 

Sulphur  in  bomb-washings  as  sulphates,  0.1045;  present  in  coal, 
0.0042;  burned  in  pyrites,  0.1003;  hence  this  experiment  gave  5150 
units  for  the  heat  due  to  a  unit  of  sulphur  as  pyrites. 

Of  course,  these  two  results  do  not  "check"  very  well,  as  all  the 
errors  of  the  test  accumulated  in  the  differences  found;  but  it  seems 
safe  to  conclude  that  the  heat  due  to  the  combustion  of  pyrites  in  the 
bomb  is  somewhere  about  5500  units  per  unit  of  sulphur.  Of  course 
the  sulphur  is  here  burned  to  S03 ,  or  rather  to  dilute  H2S04 ,  and 
gives  more  heat  than  when  it  burns  in  air  to  S02.  Pyrites  contains 
53.3$  S.  Translating  the  above  result  (5500)  into  heat  developed  per 
unit  of  FeS2  gives  2931  heat  units. 


*  By  Prof.  N.  W.    Lord.     Trans.  Am.    Inst.    Mining   Engineers,   vol.    xxvii. 
1897,  p*  960. 


-36  STEAM-VOILE Ll  ECONOMY. 

Berthelot  gives  for  the  heat  of  formation  of  dilute  H2S04  what  is 
equivalent  to  4388  units  per  unit  of  sulphur;  and  assuming  1582  as 
the  heating  value  of  iron  burned  to  magnetic  oxide  (Andrews),  a 
calculation  for  the  heating  value  of  pyrites  would  give: 

0.533S 2339 

0.467  Fe 739 

Calculated  beat 3078 

The  S  being  burned  to  dilute  H2S04. 

This  corresponds  to  the  value  found  well  enough  to  show  that 
when  pyrites  burns,  the  iron  and  sulphur  give  nearly  the  same  heat 
they  do  when  burned  separately  in  the  free  state,  which  justifies  the 
introduction  into  Dulong's  formula  of  the  sulphur  term.  As  to  the 
number  I  have  adopted  in  the  formula  (2250)*  for  the  heat  developed 
when  S  burns  to  S02 ,  it  was  taken  as  an  average  of  several  published 
figures,  and  is  probably  a  little  too  high,  but  not  enough  out  of  the 
way  to  affect  the  results  noticeably,  especially  as  the  heat  due  to  the 
combustion  of  the  iron  was  omitted,  which  it  would  appear  should 
have  been  included,  though  it  would  have  amounted  to  very  little. 

II.   HYGKOMETRIC  PROPERTIES  OF  COALS,  f 

Two  lines  of  investigation  were  undertaken  for  the  purpose  of 
•ascertaining  the  relative  qualities  of  various  coals  when  in  the  same 
physical  condition  with  reference  to  absorbing  moisture  from  the 
atmosphere : 

First,  a  number  of  samples  of  different  coals  were  reduced  to  a 
uniform  physical  condition  by  grinding  or  powdering;  were  then 
thoroughly  dried,  and  afterward  simultaneously  exposed  to  a  saturated 
or  nearly  saturated  atmosphere,  for  a  period  of  from  six  to  eight 
days  as  required,  to  obtain  constant  weight.  The  weight  of  moisture 
was  determined  by  taking  the  difference  between  the  first  and  final 
weights,  and  this  result  was  checked  by  thoroughly  drying  and  re- 
iveighing. 

Second,  an  investigation  was  made  to  determine  the  effect  of  the 
size  of  particles  upon  the  power  to  absorb  moisture;  the  investigation 
being  similar  in  nature  to  that  previously  described. 

The  method  of  drying  in  all  cases  was  the  same.  The  coal  was 
Cheated  to  a  temperature  of  from  220  to  240  degrees  Fahr.,  and  main- 
tained in  that  condition  for  one  hour. 

Results  indicate  a  great  difference  in  the  absorptive  power  of  dif- 
ferent coals  when  in  the  same  physical  state,  but  show,  however,  a 
striking  similarity  in  this  respect  of  coals  which  are  known  to  pos- 
sess similar  qualities  from  the  same  geographical  districts. 

*  The  beat-units  in  tbis  paper  are  calories  per  gram.  2250  calories  per 
gram  =  4050  B.  T.  U.  per  Ib. 

f  From  a  paper  by  Prof.  R.  C.  Carpenter  in  Trans.  A  S.  M.  E.,  vol.  xviii. 
p.  9H8. 


FUEL  AND   COMBUSTION.  3T 

The  first  investigation  seemed  to  indicate  that,  independent  of  the 
physical  condition,  different  coals  vary  greatly  in  their  hygrometrical 
properties,  and  that  with  few  exceptions,  the  power  of  absorbing  and 
retaining  moisture  is  less  as  the  calorific  value  is  greater. 

Thus  the  results  show  that  the  maximum  amount  of  moisture 
which  would  be  absorbed  by  coals  powdered  so  as  to  pass  No.  80  sieve 
were  on  the  various  tests  as  follows : 

Anthracites.  — 10  samples,  4.66  to  6.37$;  average,  5.60$. 
Eastern  Coking  Coals. — 6  samples,  0.69  to  8.16$;  average,  1.92$. 
Illinois  and  Indiana  Coals. — 6  samples,  4.65  to  14.10$;  average,  9  77$. 

The  effect  of  the  size  of  particle  is  quite  decided.  The  larger  the 
particle  the  less  the  weight  of  moisture  which  is  absorbed.  This 
indicates  that  the  absorptive  power  is  in  part  due  to  capillary  action 
of  the  surface. 

In  the  second  investigation  the  pieces  of  coal  were  made  as  nearly 
equal  as  possible  considering  their  irregular  shape  of  definite  sizes, 
having  'diameters  respectively  one  inch,  half  inch,  quarter  inch  and 
powdered  so  as  to  pass  through  sieves  of  GO  to  the  inch.  In  these  ex- 
periments there  were  used  two  samples  of  anthracite  coal,  one  ob- 
tained by  breaking  up  pieces  of  egg  coal,  the  other  pieces  of  pea  coal; 
two  specimens  of  bituminous  coal,  one  an  Illinois  coal  and  the  other 
a  Cumberland  coking  coal.  The  results  of  this  investigation,  given 
below,  show  an  increase  in  absorptive  power  as  the  size  of  the  particle 
is  diminished. 

Size  1  in.  J^in.  J^in.  Fine. 

Illinois 4.55  5.80  5.26  9.30 

Cumberland 2.17  3.76  5.61  6.42 

Lebigb  anthracite  egg 1.39  2.03  2.55  5.95 

pea .62  .66  1.31  1.59 

The  results  are  slightly  irregular,  due  probably  to  irregularities  in 
the  samples  selected,  but  the  variation,  however,  is  no  more  than 
would  probably  be  found  in  the  selection  of  samples. 

In  connection  with  the  drying  of  coals  at  temperatures  above  the 
boiling  point  a  number  of  experiments  were  made  to  determine 
whether  there  was  any  sensible  loss  of  volatile  matter,  but  so  far  as 
could  be  determined  by  repeated  trials  alternately  drying  and  moisten- 
ing and  by  varying  time  of  drying  from  one  to  three  hours,  no  loss  of 
volatile  matter  could  be  detected,  and  it  seems  exceedingly  probable 
that  no  loss  of  importance  occurs  at  temperatures  below  300  degrees 
Fahr. 

.  For  this  reason  it  would  seem  entirely  safe  to  use  this  method  of 
drying  coals  in  testing-boilers,  as  it  is  easily  applied,  and  has  given 
very  satisfactory  and  uniform  results  for  the  writer  whenever  used. 


CHAPTER   III. 
COAL. 

Coal  and  Social  Progress, — The  greatest  social  phenomenon  of  the 
nineteenth  century  is  the  increase  of  wealth  of  the  people.  Accord- 
ing to  Mulhall  the  average  wealth  per  capita  in  the  United  States  in- 
creased from  $230  in  1840  to  $1039  in  1890.  A  few  years  ago  (about 
1895)  he  said:  "The  accumulation  of  wealth  in  the  United  States 
averages  $7,000,000  daily." 

Coal  is  the  principal  natural  agent  whose  use,  through  the  medium 
of  the  steam-engine  and  of  machinery  driven  by  it,  has  been  the  cause 
of  the  difference  between  the  material  civilization  of  the  latter  part  of 
the  nineteenth  century  and  that  of  all  the  centuries  that  preceded  it. 
It  is  only  since  man  has  learned  how  to  use  coal  to  do  his  work  that 
he  has  been  enabled  to  store  up  wealth  in  such  vast  amounts  as  he  is 
doing  at  the  present  time.  Man  remained  poor  throughout  all  the 
earlier  ages  because  he  had  not  learned  how  to  make  use  of  this  one 
of  Nature's  most  important  gifts. 

A  few  hundred  years  ago  he  learned  how  to  use  it  instead  of  wcod 
and  charcoal  to  keep  himself  warm  and  to  fashion  tools  in  the  black- 
smith's forge.  Only  two  hundred  years  ago,  or  in  1698,  Savery  in- 
vented an  engine  by  means  of  which  coal  was  made  to  pump  water, 
but  this  engine  never  caused  the  turning  of  a  wheel  until  1766,  and 
then  only  by  pumping  water  which  was  used  to  turn  a  water-wheel. 
In  1705  Newcomen  invented  his  engine,  but  so  far  as  is  known  it  was 
used  only  as  a  direct-acting  pump,  and  never  turned  a  wheel.  It  was 
not  until  1781  that  James  Watt  patented  his  first  rotative  engine,  the 
first  that  contained  all  the  essential  elements  of  an  engine  capable  of 
furnishing  the  motive  power  of  a  factory,  and  it  was  five  years  later 
before  he  built  his  first  successful  pair  of  engines,  50  H.P.  each,  for 
driving  a  flour-mill.  Not  until  1807  did  Fulton  complete  the  first 
commercially  successful  steamboat,  and  not  until  1829  did  Stephenson 
perfect  his  locomotive. 


COAL.  39 

The  great  function  of  the  steam-boiler  and  engine  is  the  utilization 
of  coal  to  rim  machinery,  and  the  result  of  the  invention  of  the  steam- 
engine  is  the  civilization  and  the  wealth  of  the  race  at  the  end  of  the 
nineteenth  century. 

Production  of  Coal  in  the  United  States, — The  amount  of"  coal 
mined  in  the  United  States  in  1880  was  65,757/140  gross  tons;  in 
1890,  139,351,438  gross  tons,  according  to  the  figures  of  the  census  in 
those  years;  and  in  1899,  225,103,024  gross  tons,  or  252,115,387  net 
tons,  according  to  "The  Mineral  Industry."  The  production  in  the 
several  States  in  1899  and  the  value  at  the  mines  are  given  in  the  table 
on  page  40. 

To  the  value  of  coal  at  the  mine,  averaging  $1.10  per  ton  according 
to  the  table  on  page  40,  must  be  added  the  freight  charge  to  obtain  its 
cost  to  the  consumer.  If  this  charge  averages  $1.00  per  ton,  probably 
too  low  a  figure,  it  makes  the  total  cost  of  coal  consumed  in  the  United 
States  over  500  millions  of  dollars  per  annum. 

Formation  of  Coal. — According  to  the  geologists  a  piece  of  coal  was 
many  thousands  of  years  ago  a  mass  of  damp  vegetable  fibre,  a  portion 
of  a  peat-bog.  Half  of  its  weight,  approximately,  was  water,  and  the 
other  half  would  contain,  by  analysis,  about  50$  carbon,  Qfo  hydrogen, 
40^  oxygen,  \%  nitrogen,  and  2^  ash.  During  successive  geologic  ages 
the  peat-bog  was  submerged  and  overlaid  with  mud,  which  hardened 
into  slate.  This  was  covered  with  glacial  and  alluvial  drift,  and  it  may 
have  been  tilted  and  upheaved  by  volcanic  action  or  subsidence  of  the 
earth's  crust.  It  was  subjected  to  great  pressure  and  high  temperature, 
and  underwent  a  more  or  less  complete  destructive  distillation  under 
pressure. 

The  conditions  under  which  the  distillation  of  the  peat-bogs  took 
place  were  not  alike  in  different  parts  of  the  world.  The  variable 
factors  were  time,  depth  and  porosity  of  the  overlying  strata,  pressure 
and  temperature,  disturbance  of  the  beds  by  floods  and  by  intrusion 
into  them  of  minerals,  such  as  carbonate  of  lime  held  in  solution,  or 
clay,  sand,  iron,  and  sulphur.  Therefore  the  product  of  the  distillation 
varies  in  different  locations  all  the  way  from  the  original  peat  through 
brown  coal  or  lignite,  bituminous  and  semi-bituminous  coal,  semi- 
anthracite  and  anthracite,  to  graphitic  coal.  The  last-named,  which  is 
found  in  Khode  Island,  has  nearly  all  the  volatile  hydrocarbon  gases 
and  oxygen  driven  off  from  it,  leaving  practically  only  fixed  carbon  and 
ash,  the  carbon  being  in  a  form  which  is  so  hard  to  burn  that  the  coal 
is  not  used  as  a  commercial  fuel:  while  the  first,  lignite,  is  only  one 
remove  from  the  peat  or  woody  fibre,  retaining  perhaps  a  third  of  the 


40  STEAM-BOILER  ECONOMY. 

TOTAL  PRODUCTION  OF  COAL  IN  THE  UNITED   STATES  (IN  TONS   OF   2000    LBS.). 


States. 

1899. 

Tons. 

Value  at  Mine. 

Total. 

Per  Ton. 

Bituminous: 

7,484,763 
2,300 
#913,743 
167,161 
4,747,812 
203,775 
«23,  434,445 
6,158,224 
al,  404,  442 
4,675,000 
4,096,895 
4,668,800 
5,080,248 
500,000 
o8.ltl.eil 
1,409,882 
1,000 
ai,  049,  034 
26,994 
120,597 
16,695,949 
86,8^6 
73,066,943 
3,736,134 
940,622 
882,496 
2,111.391 
1  917.607 
a!8  201,189 
4.525,207 

$7,484,763 
12,282 
1,233,553 
430,631 
8,308,671 
183,081 
18,443,946 
5,542,402 
2,106,663 
5,937,350 
5,124,248 
3,720,100 
4,318,211 
720,000 
3,582,111 
2,227,998 
3,000 
1,600,588 
37,792 
120,597 
14,191,557 
232,854 
57,722,885 
3,706,617 
1,646,088 
1,553,193 
1,372,404 
3,355.812 
11,830,773 
5,656,509 

$1.00 
5.34 
1.35 
2.58 
1.75 
0.90 
0.78 
0.90 
1.50 
1.27 
1.25 
0.80 
0.85 
1.44 
1.12 
1.58 
3.00 
1.52 
1.40 
1.00 
0.85 
2.68 
0.79 
0.99 
1.75 
1.76 
0.65 
1.75 
0.65 
1.25 

Alaska  (b)  

Indiana  

Indian  Territory  

North  Dakota  (&)         

Oregon              .  •  

Texas  (c)  

Utah     

"W^st  Virginia  

Total  bituminous        .    

191,501,350 
36,639 

59,067 
60,518,331 

€0,977,898 

$172,406,679 
$91,597 

$162,434 
$103,486,346 

$103,648,780 

$0.90 
$2.50 

$2.75 

1.71 

~~$i77i~~ 

Cannel: 

Anthracite: 

Total  anthracite  

252,115,387 

$276,147,056 

$1.10 

(a)  Fiscal  year.        (6)  All  lignite.        (c)  One-third  lignite.        (d)  One-half  lignite. 

water,  and  a  large  part  of  the  original  hydrocarbon,  or  rather  oxy- 
hydrocarbon,  since  it  contains  a  large  percentage  of  oxygen.  The 
progressive  change  in  chemical  analysis,  from  wood  to  coal,  is  shown 
in  the  two  following  tables: 


COAL.  41 


DIMINUTION  OF  H  AND 
Substance. 
"Woody  fibre          

O  IN  SERIES  FROM  WOOD  TO 

Carbon. 
52  65 

ANTHRACITE.* 
Hydrogen.         Oxygen 
5.25              42.10 
5.96              34.47 
5.27              28.69 
5.58              21.14 
5.84              19.10 
5.05                5.61) 
8.96                4.46 

59.57 

66.04 

73.18 

Coal  from  Belestat   secondary.  . 

75  .  06 

Coal  from  liive  de  Grier           .  .  . 

89  29 

Anthracite.  Mavenne.  transition 

formation.  .          .91.58 

PROGRESSIVE  CHANGE  FROM  WOOD  TO  GRAPHITE,  f 

Wood.     Loss.       Lignite.    Loss.      Bit.  Coal.  Loss.  Anthracite.  Loss.  Graphite.. 

Carbon 49.1     18.65       30.45     12.35        18.10    3.57        14.53     1.42  13.11 

Hydrogen..     6.3      3.25         3.05       1.85          1.20    0.93          0.27     0.14  0.13 

Oxygen 44.6     24.40       20.20     18.13          2.07     1.32          0.65    0.65  0.00 

100.0    46.30       53.70    32.33         21.37     5.82         15.45    2.21        13.24 
*  Groves  and  Thorpe's  Chemical  Technology,  vol.  i.  Fuels,  p.  58. 
f  J.  S.  Newberry  in  Johnson's  Cyclopaedia. 

We  thus  have  different  varieties  of  coal,  due  to  differences  in  the 
extent  to  which  the  volatile  gases  have  been  driven  off  from  the 
original  peat  or  other  woody  coal-forming  substance.  There  are  also 
differences  in  quality  in  each  variety,  due  to  varying  percentages  of 
ash  and  water.  The  ash,  or  earthy  matter,  in  coal  ranges  from  2  to 
over  30  per  cent  in  different  localities.  The  water  ranges  from  less 
than  \%  in  the  anthracites  up  to  14#  or  more  in  some  Illinois  coals  and 
to  25$  or  more  in  some  lignites  This  water  seems  to  be  held  by  capil- 
lary attraction,  or  some  similar  force,  within  the  particles  of  a  piece  of 
apparently  dry  coal,  so  that  it  cannot  all  be  driven  off  without  heating 
it  to  a  temperature  considerably  higher  than  212°  F.,  say  250°  to 
280°  F.  The  bituminous  coals  are  hygeoscopic,  like  wood;*  that  is, 

*  Note  on  the  Hygroscopicity  of  Wood  (from  Johnson's  Materials  of  Construc- 
tion, p.  224). — Kept  on  a  shelf  in  an  ordinary  dwelling,  wood  still  retains  8  to  10 
per  cent  of  its  weight  of  water.  Nor  is  the  amount  of  water  in  dry  wood  constant; 
the  weight  of  a  panful  of  shavings  varies  with  the  time  of  day,  being  on  a  summer 
day  greatest  in  the  morning  and  least  in  the  afternoon. 

Desiccating  the  air  with  chemicals  will  cause  the  wood  to  dry,  but  wood  thus 
dried  at  80°  F.  will  still  lose  water  in  the  kiln.  Wood  dried  at  120°  F.  loses  water 
still  if  dried  at  200°  F.,  and  this  again  will  lose  more  water  if  the  temperature  is 
raised.  Absolutely  dry  wood  cannot  be  obtained  ;  chemical  destruction  sets  in 
before  all  water  is  driven  off. 

On  removal  from  the  kiln  the  wood  at  once  takes  up  water  from  the  air,  even 
in  the  driest  weather.  At  first  the  absorption  is  quite  rapid;  at  the  end  of  a  week 
a  short  piece  of  pine.  \\  in.  thick,  has  reamed  two-thirds  of,  nnd  in  a  few  months 
all,  the  moisture  it  has  when  air-dry,  8  to  10  p-T  cent,  and  also  its  former  dimen- 
sions. 


42  STEAM-BOILEX  ECONOMY* 

they  absorb  moisture  from  the  atmosphere,  and  the  quantity  they  will 
contain  depends  not  only  on  the  nature  of  the  coal,  but  on  the  relative 
humidity  of  the  atmosphere,  which  changes  from  day  to  day. 

Classification  of  Coal. — It  is  convenient  to  classify  the  several  vari- 
eties of  coal  according  to  the  relative  percentages  of  carbon  and  volatile 
matter  contained  in  their  combustible  portion  as  determined  by  prox- 
imate analysis.  The  following  is  such  a  classification : 

Fixed  Volatile  Heatjng  Value  per          Value  of 

Carbon.  Matter.  Ib.  Combustible.        Combustible 

Semi-bit.  =  100. 

Anthracite 97     to  92.5  3     to    7.5  14,600  to  14,800  93 

Semi-anthracite 92.5  to  87.5  7.5  to  12.5  14,700  to  15,000  94 

Seim-bituminous 87.5  to  75  12.5  to  25  15,500  to  16,000  100 

Bituminous,  Eastern.  75     to  60  25     to  40  14,800  to  15,200  95 

Western  65     to  50  35     to  50  13,500  to  14,800  90 

Lignite under  50            over  50  1 1,000  to  13,500  77 

The  locations  in  which  the  several  classes  of  coal  are  found  are 
described  in  some  detail  in  the  chapter  on  Coal-fields  of  the  United 
States.  The  anthracites,  with  some  unimportant  exceptions,  are  con- 
fined to  three  small  fields  in  eastern  Pennsylvania.  The  semi- anthracites 
are  found  in  a  few  small  areas  in  the  western  part  of  the  anthracite  field. 
The  semi-bituminous  coals  are  found  in  a  narrow  strip  of  territory,  20 
miles  wide  or  less,  on  the  eastern  border  of  the  great  Appalachian  coal- 
iield,  extending  from  north-central  Pennsylvania  across  the  south- 
ern boundary  of  Virginia  into  Tennessee,  a  distance  of  over  300  miles. 

It  is  a  peculiarity  of  these  semi-bituminous  coals  that  their  com- 
bustible portion  is  of  remarkably  uniform  composition,  the  volatile 
matter  usually  ranging  between  18  and  22  per  cent  of  the  combustible, 
and  approaching  in  its  analysis  marsh-gas,  CH4 ,  with  very  little  oxygen. 
They  are  usually  low  also  in  moisture,  ash,  and  sulphur,  and  rank 
among  the  best  steam-coals  in  the  world.  The  Eastern  bituminous 
coals  occupy  the  remainder  of  the  Appalachian  coal-field,  from  Pennsyl- 
vania and  eastern  Ohio  to  Alabama.  They  are  higher  in  volatile  matter, 
ranging  from  25  to  over  40  per  cent,  the  higher  figures  in  the  western 
portion  of  the  field.  The  volatile  matter  is  of  lower  heating  value, 
being  higher  in  oxygen.  The  Western  bituminous  coals  and  lignites 
are  found  in  most  of  the  States  west  of  Ohio.  They  are  higher  in 
volatile  matter  and  in  oxygen  and  moisture  than  the  bituminous  coals 
of  the  Appalachian  field,  and  usually  give  off  a  denser  smoke  when 
burned  in  ordinary  furnaces. 


COAL.  43 

Caking  and  Non-caking  Coals.  —  Bituminous  coals  are  sometimes 
classified  as  caking  and  non-caking  coals,  according  to  their  behavior 
when  subjected  to  the  process  of  coking.  The  former  undergo 
an  incipient  fusion  or  softening  when  heated,  so  that  the  fragments 
coalesce  and  yield  a  compact  coke,  while  the  latter  (also  called  free- 
burning)  preserve  their  form,  producing  a  coke  which  is  only  service- 
able when  made  from  large  pieces  of  coal,  the  smaller  pieces  being  in- 
coherent. The  reason  of  this  difference  is  not  clearly  made  out,  as 
non-caking  coals  are  often  of  very  similar  ultimate  chemical  composi- 
tion to  those  in  which  the  caking  property  is  very  highly  developed. 
It  is  found  that  caking  coals  lose  that  property  -when  exposed  to  the 
air  for  a  lengthened  period,  or  by  heating  to  about  570°  F.,  and  that 
the  dust  or  slack  of  non-caking  coal  may,  in  some  instances,  be 
converted  into  a  coherent  cake  by  exposing  it  suddenly  to  a  very  high 
temperature.  Some  coals  which  cannot  be  made  into  coke  in  the  bee- 
hive oven  are  easily  coked  in  modern  gas-heated  ovens. 

Long-flaming  and  Short-flaming  Coals.  —  The  distinction  between 
long-flaming  and  short-flaming  coals  is  one  commonly  made  by  Eu- 
ropean writers,  but  it  is  not  often  made  in  this  country.  A  long- 
flaming  coal  is  simply  one  having  a  high  percentage  of  volatile  matter, 
and  which  gives  off  a  long  flame  when  burned  in  an  ordinary  furnace 
on  account  of  the  difficulty  of  supplying  the  volatile  matter  with  a 
sufficient  quantity  of  hot  air  to  cause  its  complete  combustion. 

Bituminous  Coal  contains  no  Bitumen.  —  The  solvents  for  bitu- 
minous substances,  such  as  bisulphide  of  carbon  and  benzole,  have  no 
effect  upon  bituminous  coals. 

Cannel-coals  are  bituminous  coals  that  are  higher  in  hydrogen  than 
ordinary  coals.  They  are  valuable  as  *•'  enrichers  "  in  gas-making. 

ULTIMATE   ANALYSES    OF   SOME   CANNEL-COALS. 

COMBUSTIBLE. 


C.  H.  O+N.  S.          Ash.  c.            H. 

Boghead,  Scotland....    63.10  -8.91       7.25  0.96     19.78  79.61  11.24  9.15 

Albertite,  Nova  Scotia.    82.67  9.14      8.19  ........  82.67  9.14  8.19 

Tasmanite,  Tasmania.  .    79.84  10.41      4.93  5.32       ____  83.80  10.99  5.21 

LIGNITE   OR  BROWN   COAL    (HIGH   IN   OXYGEN). 

Cologne  .............    63.29      4.98    26.24     ....       8.49    66.97      5.27  27.76 

Bovey,  Devonshire.  ...    66.31      5.63    23.43    2.36      2.36    69.53      5.90  24.57 

Trifail,  Styria  ........    50.72      5.34    35.98    0.90      7.86    55.11       5.80  39.09 

The  above  analyses  do  not  give  the  water  or  hygroscopic  moisture. 

Lignite   or   Brown  Coal   includes   all  varieties  which   are  inter- 
mediate in  properties  between  peat  and  coal  of  the  older  formations. 


44  STEAM-BOILER  ECONOMY. 

It  is  usually  of  brownish  color,  is  non-caking,  and  high  in  moisture 
and  ash.  The  best  varieties  are  black  and  pitchy  in  lustre  and 
scarcely  to  be  distinguished  in  appearance  from  true  coals.  They  con- 
tain large  proportions  of  water  and  of  oxygen,  and  their  heating  value 
is  therefore  much  lower  than  that  of  the  true  coals. 

Ash. — The  composition  of  ash  approximates  to  that  of  fire-clay, 
with  the  addition  of  ferric  oxide,  sulphate  of  lime,  magnesia,  potash, 
and  phosphoric  acid. 

White-ash  coals  are  generally  freer  from  sulphur  than  the  red-ash 
coals,  which  contain  iron  pyrites,  but  there  are  exceptions  to  this  rule, 
as  in  a  coal  from  Peru  which  contains  more  than  10  $  of  sulphur  and 
yields  not  a  small  percentage  of  white  ash.  In  it  the  sulphur  occurs 
in  organic  combination,  but  it  is  so  firmly  held  that  it  can  only  be 
partially  expelled,  even  by  exposure  to  a  very  high  heating  out  of 
contact  with  the  air. 

The  fusibility  of  ash  varies  according  to  its  composition.  It  is  the 
more  infusible  the  more  nearly  its  composition  approaches  to  fire-clay, 
or  silicate  of  alumina,  and  becomes  more  fusible  with  the  addition  of 
other  substances,  such  as  iron,  lime,  etc.  Coals  high  in  sulphur  usually 
give  a  very  fusible  ash,  on  account  of  the  iron  with  which  the  sulphur 
is  in  combination.  A  fusible  ash  tends  to  form  clinker  upon  the 
grate-bars,  and  therefore  is  objectionable. 

Heating  Value  of  Coal. — The  heating  value  of  different  varieties  of 
coal,  together  with  the  relation  of  the  heating  value  to  chemical  com- 
position, will  be  treated  at  length  in  the  chapter  on  Heating  Value  of 
Coal,  but  a  brief  statement  of  the  subject  is  given  below,  copied  from 
an  article  by  the  author  in  "Mines  and  Minerals,"  October  1898. 

The  total  heating  value  of  coal,  measured  in  British  thermal  units, 
per  pound,  is  largely  a  question  of  geography.  It  depends  on  the  district 
in  which  the  coal  is  mined.  It  also  depends  on  the  percentage  of  ash 
in  the  coal,  which  varies  with  individual  mines  of  the  district,  with 
parts  of  the  same  mine,  and  with  the  care  taken  in  mining.  With- 
anthracite  coals  it  depends  on  the  size,  the  larger  sizes  having  the  least, 
ash. 

Coal  is  composed  of  four  different  things,  which  may  be  separated 
by  proximate  analysis,  viz.,  fixed  carbon,  volatile  hydrocarbon,  ash,, 
and  moisture.  In  making  a  proximate  analysis  of  a  weighed  quantity, 
such  as  a  gram  of  coal,  the  moisture  is  first  driven  off  by  heating  it  to- 
250°  or  300°  F.,  then  the  volatile  matter  is  driven  off  by  heating  it  in. 
a  closed  crucible  to  a  red  heat,  then  the  carbon  is  burned  o  it  of  the 


COAL. 


remaining  coke  at  a  white  heat,  with  sufficient  air  supplied,  until 
nothing  is  left  but  the 'ash. 

The  fixed  carbon  has  a  constant  heating  value  of  about  14,600 
B.T.U.  per  Ib.  The  value  of  the  volatile  hydrocarbon  depends  on 
its  composition,  and  that  depends  chiefly  on  the  district  in  which  the 
coal  is  mined.  It  may  be  as  high  as  21,000  B.T.U.  per  Ib.,  or  about 
the  heating,  value  of  marsh-gas,  in  the  best  semi-bituminous  coals,  which 
contain  very  small  percentages  of  oxygen,  or  as  low  as  10,000  B.T.U. 
per  Ib.,  as  in  those  from  some  of  the  Western  States,  which  are  high  in 
oxygen.  The  ash  has  no  heating  value,  and  the  moisture  has  in  effect 
less  than  none,  for  its  evaporation  and  the  superheating  of  the  steam 
made  from  it  to  the  temperature  of  the  chimney-gases  absorb  some  of 
the  heat  generated  by  the  combustion  of  the  fixed  carbon  and  volatile 
matter. 

The  analysis  of  a  coal  may  be  reported  in  three  different  forms,  as 
percentages  of  the  moist  coal,  of  the  dry  coal,  or  of  the  combustible. 
Thus,  suppose  one  gram  of  coal  is  analyzed,  and  the  first  heating 
shows  a  loss  of  weight  of  0.1  gram,  the  second  of  0.3  gram,  the  third 
0.5  gram,  the  remainder,  or  ash,  weighing  0.1  gram,  the  complete 
report  would  be  as  follows : 


Per  cent  of  the 
Moist  Coal. 

Per  cent  of  the 
Dry  Coal. 

Per  cent  of  the 
Combustible. 

Moisture  

10 

Volatile  matter  

30 

33  33 

37  50 

Fixed  carbon 

50 

55  56 

«o  F^n 

Ash     .,           .... 

10 

11  11 

100 

100.00 

100.00 

The  relation  of  the  volatile  matter  and  of  the  fixed  carbon  in  the 
•combustible  portion  of  the  coal  enables  us  to  judge  the  class  to  which 
the  coal  belongs,  as  anthracite,  semi-anthracite,  semi-bituminous,  bitu- 
minous, or  lignite.  Coals  containing  less  than  7.5$  volatile  matter  in 
the  combustible  would  be  classed  as  anthracite,  between  7.5  and  12.5 
per  cent  as  semi-anthracite,  between  12.5  and  25  per  cent  as  semi-bitu- 
minous, between  25  and  50  per  cent  as  bituminous,  and  over  50$  as 
lignitic  coals  or  lignites. 

The  figures  in  the  second  column,  representing  the  percentages  in 
the  dry  coal,  are  usetul  in  comparing  different  lots  of  coal  of  one  class, 
and  they  are  better  for  this  purpose  than  the  figures  in  the  first  column, 
lor  the  moisture  is  a  variable  constituent,  depending  to  a  large  extent 


STEAM-BOILER  ECONOMY. 


GOAL.  47 

on  the  weather  to  which  the  coal  has  been  subjected  since  it  was  mined, 
on  the  amount  of  moisture  in  the  atmosphere  at  the  time  when  it  is 
analyzed,  and  on  the  extent  to  which  it  may  have  accidentally  been  dried 
during  the  process  of  sampling. 

The  heating  value  of  a  coal  depends  on  its  percentage  of  total  com- 
bustible matter,  and  on  the  heating  value  per  pound  of  that  combusti- 
ble. The  latter  differs  in  different  districts  and  bears  a  relation  to 
the  percentage  of  volatile  matter.  It  is  highest  in  the  semi-bituminous 
coals,  being  nearly  constant  at  about  15,750  B.T.U.  per  Ib.  It  is 
between  14,500  and  15,000  B.T.U.  in  anthracite,  and  ranges  from 
15,500  down  to  13,000  or  less  in  the  bituminous  coals,  decreasing 
usually  as  we  go  westward,  and  as  the  volatile  matter  contains  an 
increasing  percentage  of  oxygen. 

Table  of  Heating  Values  of  Coals.  —The  table  of  proximate  analyses 
and  heating  values  of  American  coals  on  page  46  was  compiled  by 
the  author  for  the  1898  edition  of  the  Babcock  &  Wilcox  Co/s  book, 
"Steam."  The  analyses  are  selected  from  various  sources,  and  in 
general  are  averages  of  many  samples.  The  heating  values  per  pound 
of  combustible  are  either  obtained  from  direct  calorimetric  determina- 
tions or  calculated  from  ultimate  analyses,  except  those  marked  (?), 
which  are  estimated  from  the  heating  values  of  coals  of  similar  com- 
position. The  figures  in  the  last  column  are  obtained  by  dividing  the 
figures  in  the  preceding  column  by  905.7,  the  number  of  heat-units 
required  to  evaporate  a  pound  of  water  at  212°  into  steam  of  the  same 
temperature. 

The  heating  values  per  pound  of  combustible  given  in  the  table, 
except  those  marked  (?),  are  probably  within  3$  of  the  average  actual 
heating  values  of  the  combustible  portion  of  the  coals  of  the  several 
districts.  When  the  percentage  of  moisture  and  ash  in  any  given  lot 
of  coal  is  known  the  heating  value  per  pound  of  coal  may  be  found 
approximately  by  multiplying  the  heating  value  per  pound  of  combus- 
tible of  the  average  coar  of  the  district  by  the  difference  between  100$ 
and  the  sum  of  the  percentages  of  moisture  and  ash. 

In  1892  the  author  deduced  from  Mahler's  tests  on  European  coals 
a  table  of  the  approximate  heating  value  of  coals  of  different  composi- 
tion, which  is  given,  somewhat  modified,  below.  (Trans.  A.  S.  M.  E., 
vol.  xx.  p.  337.) 

The  experiments  of  Lord  and  Haas  on  American  coals  (Trans.  Am. 
lust.  Mining  Engineers,  1897)  practically  confirm  these  figures  for  all 
coals  in  which  the  percentage  of  fixed  carbon  is  60$  and  over  of  the 


48 


STEAM-BOILER  ECONOMY. 


APPROXIMATE  HEATING  VALUE  OF  COALS. 


Per  cent 
Fixed  Carbon 

Heating  Value  per  Ib. 
Combustible. 

Per  cent 
Fixed  Carbon 

Heating  Value  per  Ib. 
Combustible. 

in  Coal 

in  Coal 

Dry  and  Free 

Dry  and  Free 

from  Ash. 

B.  T.  U. 

Calories. 

from  Ash. 

B.  T.  U. 

Calories. 

100 

14,600 

8,100 

68 

15,480 

8,600 

97 

14,940 

8,300 

63 

15,120 

8,400 

94 

15,210 

8,450 

60 

14,580 

8,200 

90 

15,480 

8,600 

57 

14,040 

7,900 

87 

15,660 

8,700 

55 

13,320 

7.700 

80 

15,840 

8,800 

53 

12,600 

7,400 

72 

15,660 

8,700 

51 

12,240 

6,900 

•combustible,  but  for  coals  containing  less  than  60$  fixed  carbon  or 
more  than  40$  volatile  matter  in  the  combustible  they  are  liable  to  an 
error  in  either  direction  of  about  4$.  It  appears  from  these  experi- 
ments that  the  coal  of  one  seam  in  a  given  district,  where  the  ratio  of 
the  volatile  matter  to  the  total  combustible  is  uniform,  has  the  same 
heating  value  per  pound  of  combustible,  within  one  or  two  per  cent,  but 
that  coals  of  the  same  proximate  analysis,  and  containing  over  40$ 
volatile  matter,  but  mined  in  diiferent  districts,  may  differ  6  or  8  per 
cent  in  heating  value. 

It  will  be  noticed  that  the  coals  containing  from  72  to  87  per  cent 
•of  fixed  carbon  in  the  combustible  have  practically  the  same  heating 
value.  This  is  confirmed  by  Lord  and  Haas's  tests  of  Pocahontas  coal. 
A  study  of  these  tests  and  of  Mahler's  indicates  that  the  heating  value 
of  all  the  semi-bituminous  coals,  75  to  87.5  per  cent  fixed  carbon,  is 
within  1£$  of  15,750  B.T.U.  per  Ib. 

The  heating  value  of  any  coal  may  also  be  calculated  from  its  ulti- 
mate analysis,  with  a  probable  error  not  exceeding  2$  (except  in  the 
•cases  of  cannel-coal  and  some  lignites  in  which  the  error  may  be 
.greater)  by  the  following  formula: 


Heating  value  per  Ib.  =  146C  +  620  H  -     . 


in  which  C,  H,  and  0  are  respectively  the  percentages  of  carbon, 
hydrogen,  and  oxygen.  This  formula  is  known  as  Dulong's.  Its 
approximate  accuracy  is  proved  by  both  Mahler's  and  Lord  and  Haas's 
experiments,  and  any  deviation  of  the  calorimetric  determination  of 
any  ordinary  coal  more  than  2$  from  that  calculated  by  the  formula 
is  more  likely  to  proceed  from  an  error  in  either  the  calorimetric  test 
or  the  analysis  than  from  an  error  in  the  formula. 


COAL. 


Mr.  E.  S.  Hale,  in  circular  No.  5  of  the  Mutual  Boiler  Insurance 
Co.,  1898,  gives  the  following  table  showing  the  heating  value  of  dif. 
f erent  coals : 

HEATING   VALUE   OF  VARIOUS  COALS.      COMBUSTIBLE   PORTION   ONLY  CONSIDERED. 


Coal. 

Lehigh 
Anthracite. 

Schuylkill 
Anthracite. 

Wyoming 
Anthracite. 

Lykens 
Valley 
Anthracite. 

Per  cent  fixed  carbon  in  fuel. 

96.6 

95.5 

95 

91 

Relative  steam-making  value. 
Steam  Users'  Association  Circular  3        .... 

92 

95 

97 

97 

Calorific  power  computed  from    proximate 
analyses  by  Kent's  table,  B.  T.  U  
Relative 

14.850 
94 

15,000 
95 

15,100 
95  5 

15,400 
97 

Calorific  power  computed  by  Dulong's  for- 
mula from  ultimate  analyses  B  T  U. 

14,255 

15395 

Relative 

92.5 

99  g 

Calorific  power  from  another  set  of  analyses, 
B  T  U 

14  755 

15  380 

Relative 

95 

100  4 

Calorific  power  Barrus  calorimeter,  B.  T.  U.. 
Relative...           

Coal. 

Cumber- 
land 
Semibitu- 
minous. 

Pocahon- 
tas. 

New 
River. 

Clear- 
field. 

Nova 
Scotia. 

Per  cent  fixed  carbon  in  fuel. 
Average  of  a  number  of  analyses        . 

81 

78  7 

76  2 

76 

KQ 

Relative  steam-making  value. 
Steam  Users'  Association  Circular  3  
-Calorific    power  computed  from    proximate 
analyses  by  Kent's  table,  B.  T.  U  
Relative 

100 

15,840 
100 

102 

15,840 
100 

95 

15,780 

QQ 

97 

15,780 
QQ 

85 

14,150 
8Q 

Calorific  power  computed  by  Dulong's  for- 
mula from  ultimate  analyses,  B.  T.  U  

15,400 

15,552 

15,623 

14,240 

Relative  

100 

101 

101  5 

93 

Calorific  power  from  another  set  of  analyses, 
B.  T.  U  . 

15  320 

15  691 

15  104 

14  515 

Relative            ... 

100 

102  4 

98  6 

«... 

94  7 

Calorific  power  Barrus  calorimeter,  B.  T.  U.. 

14,440 

14,761 

14.540 



13  068 

Relative  

100 

102  2 

100  8 

90  4 

The  relative  values  are  found  by  assuming  Cumberland  100#. 

The  figures  obtained  by  the  Barrus  calorimeter  are  clearly  in  error.. 
They  are  far  below  those  obtained  on  similar  coals  by  the  Mahler 
calorimeter,  and  also  below  the  calculated  values. 

Errors  in  Reported  Heating  Values  of  Coals. — Errors  in  sampling 
and  in  the  calorimetric  test  are  quite  common,  and  the  error  of  the  latter 
is  almost  always  in  the  direction  of  making  the  reported  heating  value 
of  a  coal  too  small.  The  effect  of  this  error  is  to  make  the  apparent 
efficiency  of  a  boiler  tested  with  this  coal  higher  than  the  real  efficiency. 
Whenever  the  efficiency  reported  is  high  and  at  the  same  time  the 
reported  heating  value  of  the  fuel  per  pound  of  combustible  is  more 
than  2  per  cent  lower  than  the  figures  in  the  table  on  page  46  for  coal 
from  the  same  district,  the  results  should  be  looked  on  with  suspicion. 


50  STEAM-BOILER  ECONOMY. 

Further  information  on  this  subject  will  be  found  in  a  paper  by  the 
author  entitled  "The  Efficiency  of  a  Steam-boiler:  What  is  it?"  in 
Trans.  Am.  Soc.  Mechanical  Engineers,  vol.  xvii.  p.  645. 

The  efficiency  commonly  obtained  in  practice  in  the  Western  States 
with  bituminous  coals  burned  in  ordinary  furnaces  is  not  over  60$, 
and  is  often  less  than  50$.  Probably  55$  is  a  fair  average.  The 
highest  efficiency  obtainable  under  the  best  conditions,  with  mechani- 
cal stokers  and  with  furnaces  adapted  to  burn  the  volatile  matter  of 
the  coal,  is  about  75$.  The  difference,  -20$-j-75$  —  26f$,  is  the  margin 
for  saving.  If  only  half  of  this  saving,  or  13^$,  can  be  made,  and  this 
is  easily  possible  by  the  introduction  of  improved  methods  of  burniDg 
AVestern  coals,  the  reduction  of  the  cost  of  coal  used  for  steam  purposes, 
were  these  improvements  generally  adopted,  would  amount  to  many 
millions  of  dollars  a  year.  This  is  the  most  important  improvement 
that  can  be  made  in  existing  American  boiler  practice. 

Halation  of  Quality  of  Coal  to  the  Capacity  and  Economy  of  a 
Boiler. — The  actual  evaporating  capacity  of  a  boiler  containing  a 
given  amount  of  heating  surface  and  a  given  area  of  grate  depends 
primarily  upon  the  quantity  of  heat  which  may  be  generated  in  the 
furnace.  This  depends  on  the  quantity  of  coal  that  may  be  burned, 
and  also  on  its  quality.  The  better  the  quality  the  greater  number 
of  heat-units  will  be  generated  by  the  combustion  of  each  pound.  If 
the  coal  is  high  in  moisture  or  in  oxygen,  not  only  will  the  heat-units 
derived  from  a  pound  of  it  be  low,  but  the  attainable  temperature  will 
also  be  lower  than  that  attainable  from  a  better  coal;  and  furnace 
temperature,  as  will  be  shown  in  another  chapter,  is  an  important 
factor  of  both  capacity  and  economy. 

If  the  coal  is  high  in  ash,  not  only  is  its  value  per  ton  diminished, 
but  the  quantity  of  ash  formed  on  the  grate  tends  to  check  the  air- 
supply,  and  therefore  to  diminish  the  rate  of  combustion,  and  conse- 
quently the  quantity  of  steam  generated.  If  the  coal  is  high  in 
sulphur,  the  ash  will  be  apt  to  fuse  into  clinker,  and  this  may  choke 
the  grates  completely,  necessitating  frequent  cleaning  of  the  fire. 

In  order  to  develop  the  rated  capacity  of  a  boiler  with  poor  coal 
high  in  ash,  it  is  necessary  to  have  either  a  larger  grate  surface  or 
stronger  draft  than  with  good  coal.  Sometimes  strong  draft  is  of  no 
avail,  on  account  of  the  clinkering  of  the  ash,  and  in  such  a  case  large 
grate  surface  is  absolutely  required. 

The  quality  of  coal,  therefore,  is  a  most  important  factor  of  both 
the  capacity  and  economy  of  a  boiler.  It  is  possible  with  a  good  free- 


COAL.  51 

burning  coal  to  obtain  from  a  given  boiler  twice  as  much  steam  as  can 
be  obtained  with  the  same  boiler  and  the  same  draft  from  poor  coal, 
and  the  relative  efficiency  obtainable  with  the  two  coals,  or  the  steam 
generated  per  pound  of  coal,  may  differ  30  or  40  per  cent. 

The  quality  of  the  coals  of  the  United  States  varies  greatly  in  dif- 
ferent districts.  In  some  limited  districts  the  very  best  quality  is  regu- 
larly found;  in  other  districts  the  quality  is  uniformly  from  good  to 
medium,  and  in  still  others  it  ranges  from  poor  to  worthless. 

To  buy  coal  on  the  reputation  of  the  district  in  which  it  is  mined 
is  not  as  good  a  way  as  to  buy  it  on  a  guarantee  of  quality,  as  deter- 
mined by  an  analysis  for  water,  volatile  matter,  ash,  and  sulphur,  but  it 
is  the  most  common  way.  A  knowledge  of  the  quality  of  coals  found  in 
different  districts  is  therefore  of  some  importance.  The  next  chapter, 
"  Coal-fields  of  the  United  States,"  is  devoted  to  this  subject. 

Valuing  Coals  by  Test  and  by  Analysis. — The  best  way  to  obtain 
the  relative  value  of  different  coals  for  any  particular  steam-boiler 
plant  is  to  have  a  car-load  of  each  coal  tested  under  the  ordinary  run- 
ning conditions  of  the  plant,  and  then  to  check  the  results  by  a  proxi- 
mate analysis  of  each.  The  coal  that  is  most  economical  for  one 
boiler-plant  is  not  necessarily  the  most  economical  for  another,  on 
account  of  the  differences  in  conditions,  such  as  kind  of  furnace,  area 
of  grate  surface,  draft  available,  etc.  A  plant  designed  for  the  pur- 
pose may  be  able  to  use  with  satisfaction  the  poorest  quality  of  the  fine 
sizes  of  anthracite,  while  another  may  not  be  able  to  use  anything 
cheaper  than  the  best  pea  coal,  and  still  another,  having  deficient  grate 
surface,  may  be  compelled  to  use  egg  size,  or  even  semi-bituminous. 

Besides  testing  the  coals  by  burning  them  under  the  boilers  and 
weighing  the  quantity  of  water  evaporated,  a  proximate  analysis  of 
each  coal  should  be  made  so  as  to  arrive  at  a  standard  of  quality 
by  reference  to  which  future  purchases  may  be  made.  A  schedule  of 
relative  values  may  then  be  prepared,  something  like  the  following: 

Anthracite  and  Semi-anthracite. — The  standard  is  a  coal  containing 
5$  volatile  matter,  not  over  2$  moisture,  and  not  over  10$  ash.  A  pre- 
mium of  1$  on  the  price  will  be  given  for  each  per  cent  of  volatile  matter 
above  5$  up  to  and  including  15$,  and  a  reduction  of  2$  on  the  price 
will  be  made  for  each  1$  of  moisture  and  ash  above  the  standard. 

Semi-bituminous  and  Bituminous. — The  standard  is  a  semi-bitu- 
minous coal  containing  not  over  20$  volatile  matter,  2$  moisture, 
6$  ash.  A  reduction  of  1$  in  the  price  will  be  made  for  each  1$  of 
volatile  matter  in  excess  of  25$,  and  of  2$  for  each  1$  of  ash  and 
moisture  in  excess  of  the  standard.  b 


CHAPTER  IV. 

COAL-FIELDS  OF  THE  UNITED  STATES.  -• 

THE  accompanying  maps  showing  the  developed  coal-fields  of  the 
United  States  are  copied  from  one  that  was  published  in  the  Reports 
of  the  Census  of  1890. 

The  long  field  extending  southwesterly  from  north-central  Penn- 
sylvania to  near  the  c'entre  of  Alabama  is  the  great  Appalachian 
field,  which  contains  in  a  narrow  strip  on  its  eastern  border  the  semi- 
bituminous  coals,  and  west  of  this  strip  the  best  varieties  of  bituminous 
gas,  steam,  and  coking  coals.  East  of  this  field  there  are  several 
small  detached  fields,  the  most  important  of  which  are  the  three  an- 
thracite fields  of  eastern  Pennsylvania.  To  the  north  west,  there  is  the 
separate  field  of  Michigan,  containing  a  rather  poor-quality  of  bitumi- 
nous coal.  To  the  west  is  the  Illinois  or  Central  field,  extending  into 
Indiana  and  Kentucky,  and  containing  a  great  variety  of  bituminous 
coals,  most  of  which  are  inferior  to  the  coals  of  the  Appalachian  field. 
West  of  the  Mississippi  the  principal  field  is  the  great  Missouri  field 
covering  several  States,  and  having  several  detached  portions  reaching 
into  Texas.  The  coals  of  this  field  are  mostly  of  a  poor  quality.  West 
of  the  97th  meridian  there  are  a  great  number  of  detached  fields,  mostly 
of  small  areas,  with  every  grade  of  coal  from  anthracite  to  lignite. 
The  principal  characteristics  of  the  several  fields,  and  the  quality  of  the 
coal  found  in  each,  will  be  treated  of  below. 

Graphitic  Coal  in  Rhode  Island  and  Massachusetts. — An  area  of 
400  square  miles  in  the  central  part  of  Rhode  Island  and  eastern  part  of 
Massachusetts,  from  Newport  Neck,  R.  I.,  to  Mansfield,  Mass.,  contains 
a  variety  of  anthracite  which  has  been  metamorphosed  into  graphite  or 
graphitic  coal.  It  requires  such  a  high  degree  of  heat  for  combustion 
that  it  can  be  used  only  with  other  combustible  material  or  under  a 
heavy  draft.  The  deposit  was  worked  as  early  as  1808,  at  the  Ports- 
mouth mine,  and  at  intervals  since,  but  never  with  profit. 

52 


120        127        125         123       ill        11%        117        115       113        111        109       107       I0~5      103       101       99        97 


119  II1 


109  107  105  103  101  99  7 


COAL-FIKLDS    OK    THE    UNITED    STATES   WEST    OF    THE    9~TH    MKKIDIAN. 


COAL-FIELDS  OF  THE   UNITED  STATES.  53 

ANALYSES   OP  RHODE  ISLAND  AND  MASSACHUSETTS   COAL 

Water  and  Volatile  Matter.  Fixed  Carbon.  Ash. 

Mansfield,  Mass 2  to  4  90  to  92  4 

Rhode  Island  coal 7  to  10  77  to  84  '5  to  6 

Cranston,  R.  1 8.55                  3.55  82.25  5.65 

The  Anthracite  Coal-beds  of  Pennsylvania. — These  beds  are  all  in 
the  eastern  portion  of  the  State.  They  are  three  in  number,  known 
variously  as  First,  Second,  and  Third,  as  Southern,  Middle,  and 
Northern,  or  as  Schuylkill,  Lehigh,  and  Wyoming.  The  area  of  the 
first  is  138  square  miles,  of  the  second  38  square  miles,  and  of  the 
third  196  square  miles — a  total  of  472  square  miles.  There  are  fifteen 
workable  beds  in  this  area,  of  a  total  thickness  of  107  ft.  of  coal,  the 
thickness  of  the  measures  in  which  the  beds  are  interstratified  being 
about  3000  feet.  The  coal  in  all  of  the  fields  follows  the  general  law 
of  increasing  in  percentage  of  volatile  matter  and  decreasing  in  hard- 
ness towards  the  western  portion  of  the  fields. 

In  -'Mineral  Resources "  for  1886  the  anthracite  fields  of  Penn- 
sylvania are  described  as  grouped  into  five  principal  divisions: 
(1)  The  southern  or  Pottsville  field,  extending  from  the  Lehigh  River 
at  Mauch  Chunk  southwest  to  within  a  few  miles  of  the  Susquehamia 
River  north  of  Harrisburg;  (2)  the  western  or  Mahanoy  and  Shamokin 
field,  lying  between  the  eastern  head-waters  of  the  Little  Schuylkill 
River  and  the  Susquehanna;  (3)  the  eastern  middle  or  the  upper 
Lehigh  field,  lying  between  the  Lehigh  River  and  Catawissa  Creek, 
principally  in  Luzerne  County;  (4)  the  northern  or  Wyoming  and 
Lackawanna  field,  which  lies  in  the  two  valleys  from  which  its  geo- 
graphical name  is  derived;  (5)  the  Loyalsock  and  Mehoopany  field, 
named  from  the  two  creeks  whose  head-waters  drain  it.  The  latter  is 
a  small  field  about  20  or  25  miles  northwest  of  the  western  end  of  the 
northern  field. 

In  addition  to  this  geological  division  the  fields  are  also  subdivided 
under  different  names  and  in  a  different  way  for  trade  purposes,  the 
divisions  being  known  as  trade  regions.  These  are:  (1)  The  Wyoming 
region,  embracing  the  entire  northern  and  Loyalsock  fields;  (2)  the 
Lehigh  region,  embracing  all  of  the  eastern  middle  field  and  the  Pan- 
ther Creek  district  of  the  southern  field;  and  (3)  the  Schuylkill  region, 
embracing  the  western  middle  field  and  all  of  the  southern  field  except 
the  Panther  Creek  district. 

Sizes  of  Anthracite  Coal. — Much  confusion  and  inconvenience  in 
the  marketing  of  anthracite  coal  luu  been,  in  times  past,  occasioned 


.54  STEAM-L01LER  ECONOMY. 

by  the  want  of  uniformity  in  the  sizes  of  the  coal  produced.  At  a 
meeting  of  operators  from  every  part  of  the  anthracite  -fields,  held 
for  the  purpose  in  Wilkesbarre,  this  subject  was  considered,  and  the 
following  sizes  of  meshes  were  adopted,  to  take  effect  January  1,  1891 : 

Egg,  through  2J  inches  and  over  2  inches. 

Stove,  through  2  inches  and  over  1J  inches. 

Chestnut,  through  1£  inches  and  over  f  inch. 

Pea,  through  £  inch  and  over  •£  inch. 

Buckwheat,  through  £  inch  and  over  £  inch. 

No.  2  buckwheat,  through  £  inch  and  over  ^  inch. 

Semi-anthracite  in  Sullivan  Co,,  Pa. — The  Bernice  coal-basin  lies 
between  Beech  Creek  on  the  north  and  Loyalsock  Creek  on  the  south. 
It  is  six  miles  long  E.  to  W.,  and  hardly  a  third  of  a  mile  across. 
There  is  8  ft.  of  coal  in  a  bed  of  12  ft.  of  coal  and  slate.  The  coal  of 
this  bed  is  on  the  dividing  line  between  anthracite  and  semi-anthracite, 
and  is  similar  to  the  coal  of  the  Lykens  Valley  district.  Nine  analyses 
give  a  range  as  follows:  Water,  0.65  to  1.97;  volatile  matter,  3.56 
to  9.40;  fixed  carbon,  82.52  to  89.39;  ash,  3.27  to  9.34;  sulphur,  0.24 
to  1.04. 

Progression  from  Bituminous  to  Anthracite, — In  a  direction  across 
the  basins  northward  from  Bernice,  in  Sullivan  Co.,  to  Gaines,  in 
Tioga  and  Potter  counties,  a  distance  of  50  miles,  is  seen  the  transi- 
tion from  bituminous  to  anthracite  coal,  the  proportion  of  volatile 
matter  to  fixed  carbon  in  the  different  basins  being: 

Volatile  Matter.  Fixed  Carbon. 

Gaines,         1  to    1.964,  equal  to 33.7  66.3 

Blossburg,  1  "    3.494,       "        22.3  77.7 

Barclay,       1   "    4.094,       "        19.6  80.4 

Bernice,       1  "  10.289,       "        8.9  91.1 

At  Bernice  a  semi-bituminous  coal  underlies  the  semi-anthracite 
60  ft.,  both  beds  being  found  in  the  same  hillside  only  60  ft.  apart.* 
In  another  case  a  coal-bed  has  two  benches,  the  upper  semi-bituminous 
and  the  lower  anthracite,  with  6  ft.  of  slate  bottom.  (From  reports 
of  2d  Geological  Survey  of  Pennsylvania.) 

Early  Use  of  Pennsylvania  Anthracite  Coal. — Pennsylvania  anthra- 
cite coal  was  known  as  early  as  1766,  and  was  used  in  1768  in  the 
Wyoming  Valley  by  two  blacksmiths  named  Gore.  In  1776  several 
boat-loads  were  sent  to  Carlisle,  where  it  was  used  during  the  Revolu- 

*It  will  be  noted  that  this  condition  in  Sullivan  Co.,  Pa.,  is  exactly  opposite  to 
that  found  in  western  Pennsylvania  and  central  Ohio,  where  the  coals  mined  over 
a  large  extent  of  country  show  nearly  identical  composition.  See  Lord  and  Haas's 
tests  in  the  next  chapter. 


COAL-FIELDS   OF  THE   UNITED  STATES.  55 

tionary  War  to  manufacture  arms.  It  was  not  used  for  domestic  pur- 
poses until  1808,  when  Judge  Jesse  Fell  of  Wilkesbarre  burned  it  on 
an  experimental  grate  of  hickory  withes.  He  then  made  an  iron 
grate,  and  taught  the  people  in  the  vicinity  how  to  make  such  grates. 
In  1793  the  Lehigh  Coal  Mining  Co.  was  formed,  which  some  years 
later  sold  a  quantity  to  the  city  of  Philadelphia  for  the  use  of  a  steam- 
engine  at  the  water-works,  then  at  Broad  and  Market  streets,  but  it 
was  not  used  because  it  "could  not  be  burned."  In  1812  Col.  George 
Shoemaker  took  nine  wagon-loads  to  Philadelphia,  disposed  of  two  or 
three  loads  at  the  cost  of  handling,  and  left  the  rest  with  different  per- 
sons for  experiment.  At  the  Fairmount  Wire  and  Nail  Works  the  work- 
men spent  a  forenoon  in  fruitless  attempts  to  make  a  fire  with  it.  At 
last  they  closed  the  furnace  doors  and  went  to  dinner;  returning  an 
hour  later,  they  found  the  doors  red-hot  and  the  furnace  all  aglow. 
After  that  there  was  no  more  trouble  in  burning  anthracite.  In  1820 
the  trade  was  fully  established,  365  tons  being  shipped  to  Philadelphia 
in  that  year. 

The  failures  to  burn  anthracite  in  these  early  days  were  due  to 
ignorance  of  the  proper  conditions  for  burning  it.  These  are : 

1.  A  very  hot  fire  of  wood  must  first  be  established. 

2.  The  coal  should  be  laid  in  a  bed  several  inches  deep. 

3.  The  bed  of  coal  must  not  be  poked  or  otherwise  disturbed  while 
beginning  to  burn. 

4.  A  constant  supply  of  air  must  be  maintained  from  the  grate 
through  the  fire. 

An  interesting  account  of  the  early  history  of  the  anthracite  coal 
trade  will  be  found  in  "Mineral  Industry"  for  1895. 

Virginia  Anthracite.  —  In  the  southwestern  part  of  Virginia 
occur  beds  of  coal  which  on  analysis  prove  to  be  anthracite.  They 
are  found  in  Pulaski  and  Wythe  counties,  along  the  southern  border 
of  Little  Walker  Mountain.  The  areas  are  limited  and  the  coals  have 
been  greatly  disturbed.  They  do  not  belong  to  the  true  Carboniferous 
coals,  but  to  the  Upper  Devonian  (Rogers  X.)  formation,  and  lie 
under  the  true  coal-measures  of  Pennsylvania,  Ohio,  and  northwestern 
Virginia. 

Analyses  of  seven  samples  gave : 

Water.  Volatile  Matter.         Fixed  Carbon.  Ash. 

0.35  to  0.80  6  to  7.58  85.85  to  89.47  3.97  to  7.35 

Anthracite  in  Colorado. — Anthracite  coal  of  good  quality  is  found 
.in  Gunnison  Co.,  Colorado  (Hayden's  Survey  Report  for  1874).  The 


56  STEAM-BOILER  ECONOMY. 

coal  is  not  a  true  Carboniferous  anthracite,  but  is  an  "  altered  lignite  " 
of  the  Post-Cretaceous  formation.  The  quality  varies  greatly  in 
different  beds  and  even  in  the  same  bed  in  neighboring  localities, 
occurring  in  all  stages  of  transition  from  bituminous  to  hard  anthra- 
cite. The  following  are  analyses  of  some  of  these  coals.  No.  Ill 
might  be  classified  as  a  semi- bituminous  coal,  and  No.  VI  as  a  semi- 
anthracite, 

I.  II.  III.  IV.  V.  VI. 

Water 2.00  1.60  4.00)  _ft  11.64 

Volatile  matter  ....     2.50  3.40  14.00  \  K39 

Fixed  carbon 91.90  88.20  74.00  88.92        91.02  86.60 

Ash 3.60  6..80          8.00  3.68  5.30  4.37 

Anthracite  in  New  Mexico.— Dr.  E.  W.  Raymond,  formerly  U.  S. 
Mining  Commissioner,  in  his  report  for  1870  describes  a  bed  of  true 
anthracite,  4  to  5  feet  thick,  near  Santa  Fe,  containing  80.5$  of  fixed 
carbon,  and  another,  1£  miles  distant,  containing  88$  carbon  and 
5$  ash. 

BITUMINOUS  AND   SEMI-BITUMINOUS   COAL-FIELDS  OF  THE  UNITED 

STATES. 

The  following  notes  on  the  bituminous  and  semi-bituminous  coal- 
fields and  on  the  quality  of  coal  found  in  them  have  been  compiled 
from  a  variety  of  sources ;  among  others,  the  reports  of  the  U.  S. 
Census  of  1890,  the  annual  volumes  of  "Mineral  Resources  of  the 
United  States"  and  "Mineral  Industry,"  reports  of  the  Geological 
Surveys  of  Pennsylvania  and  other  States,  and  various  papers  in  the- 
Transactions  of  the  American  Institute  of  Mining  Engineers. 

The  Triassic  Area  comprises  what  is  known  as  the  Richmond  basin 
in  Chesterfield  and  Henrico  counties,  Virginia,  and  the  Deep  River 
and  Dan  River  fields  in  North  Carolina.  Charles  A.  Ashburner,  in 
"Mineral  Resources"  for  1866,  says  that  the  first  coal  mined  systemati- 
cally in  the  United  States  was  taken  from  the  Richmond  basin,  and 
that  in  1822  about  48,214  tons  of  coal  were  produced  there,  more 
than  twelve  times  the  total  amount  produced  in  the  Pennsylvania, 
anthracite  field  in  the  same  year.  Its  maximum  output  was  reached  in 
1883,  when  142,587  tons  were  mined. 

The  Bituminous  Coals  of  the  Carboniferous  Formation  (not  in- 
cluding the  more  recent  coals  of  the  Western  States)  are  found  in  four 
separate  fields  or  basins,  which  are  shown  on '  the  map,  viz. :  1.  The 
Appalachian  field,  extending  from  Pennsylvania  to  Alabama,  contain- 
ing 50,105  square  miles.  The  eastern  portion  of  the  Appalachian 


COAL-FIELDS  OF  THE   UNITED  STATES.  5? 

field  contains  the  semi-bituminous  coals,  which  are  found  in  a  narrow- 
strip  running  from  northern  Pennsylvania  through  portions  of  Mary- 
land, Virginia,  West  Virginia,  and  Tennessee.  2.  The  Illinois  basin, 
extending  into  the  western  part  of  Indiana  and  northwestern  Ken- 
tucky, 47,188  square  miles.  3.  The  Michigan  basin,  6700  square 
miles.  4.  The  Missouri  or  Western  basin,  90,343  square  miles,  cover- 
ing portions  of  Iowa,  Nebraska,  Missouri,  Kansas,  Indian  Territory,, 
and  Arkansas,  with  an  extension  into  Texas.  The  coal  in  this  basin  ia. 
in  general  not  so  pure  as  that  in  the  Appalachian  field,  and  contains  a, 
great  deal  of  sulphur. 

West  of  the  Missouri  there  are  the  lignites  and  lignitic  coals 
(some  of  them  transformed  into  bituminous  and  anthracite)  of  the 
Eocky  Mountain  field,  containing  the  coal  areas  in  the  States  and 
Territories  lying  along  the  Rocky  Mountains,  and  the  Pacific  Coast  field, 
embracing  the  coal  districts  of  Washington,  Oregon,  and  California. 

The  various  fields  are  described  at  some  length  in  "  Mineral  Re- 
sources "  for  1886,  and  also  in  the  report  for  1894.  The  latter  also 
contains  some  historical  information  regarding  the  development  of 
these  fields.  "  Mineral  Resources "  for  1892  contains  some  inter- 
esting contributions  from  State  geologists  on  the  coal-fields  of  several 
States. 

Pennsylvania. — The  Appalachian  coal-field  extends  over  portions 
of  31  counties.  It  has  a  total  area  of  12,302  square  miles  in  the  State. 

Blossburg  field,  Tioga  Co.  Five  beds,  A,  B,  C,  D,  and  E,  from 
2J  to  5£  feet  thick.  Coal  A  is  the  lowest  of  the  series.  Coal  B, 
Bloss  bed,  4|  to  5|-  feet,  is  the  best.  Coal  C  is  a  sort  of  cannel-coal 
of  an  inferior  grade  in  this  location;  farther  west  it  improves. 

Mclntyre  basin,  Lycoming  Co.  The  coal-beds  are  similar  to  those 
of  the  Blossburg  region,  three  of  them,  E,  C,  and  A,  being  of  workable 
thickness. 

Towanda  basin,  Bradford  Co.  One  seam  also  found  in  the  Mclntyre 
basin. 

Snowshoe  basin,  Centre  Co.  Eight  miles  in  length  by  four  in 
width.  Five  seams,  A,  B,  C,  D,  E.  A  has  6  to  3J  feet,  and  E  5 
feet,  of  good  coal. 

Clearfield  region,  on  Moshannon  Creek,  in  Clearfield  Co.  Threa 
workable  seams,  5,  4^,  and  4  feet.  The  latter,  coal  D,  is  principally 
worked. 

Johnstown  region.  Cambria  Co.     Five  beds,  A,  B,  C,  D,  E,  2^  to  ? 


58  STEAM-BOILER  ECONOMY. 

feet  thicK.  The  coal  is  mostly  used  iii  the  iron-  and  steel-works  in  the 
vicinity. 

Broad  Top  basin,  in  Bedford,  Huntington,  and  Fulton  counties, 
40  miles  east  of  the  Alleghauy  Mountains.  The  area  is  81  square 
miles.  Five  workable  beds,  the  principal  one  being  5  to  10  feet  thick. 

Salisbury  basin,  Somerset  Co.  A  short  extension  of  the  Cumber- 
land coal-field  of  Maryland.  It  contains  all  the  coals  of  the  Lower 
measures  and  several  square  miles  of  the  Pittsburgseam. 

Semi-bituminous  coal  is  produced  in  all  the  above-named  fields. 

Main  Field  of  Western  Pennsylvania.  One  large  field  in  the  south- 
western counties.  The  several  beds  are  found  in  different  series, 
known  respectively  as  the  Upper  Barren,  the  Upper  Productive,  the 
Lower  Barren,  and  the  Lower  Productive  coal-measures,  and  the 
Conglomerate  series. 

The  Upper  Barren  measures  contain  but  one  seam  of  commercial 
importance,  the  Washington  seam,  which  attains  its  best  developmant, 
3  to  3^  feet,  in  Washington  and  Fayette  counties. 

The  Upper  Productive  Coal-measures  contain  the  great  Pittsburg 
seam,  6  to  12  feet  thick,  in  Fayette,  Washington,  Allegheny,  West- 
moreland, and  Greene  counties,  smaller  areas  also  occurring  in 
Indiana,  Somerset,  and  Beaver  counties.  The  famous  Connells- 
ville  coke  is  made  from  this  seam.  The  Connellsville  region  is 
a  narrow  strip,  about  3  miles  wide  and  60  miles  in  length.  The 
Pittsburg  seam  here  affords  from  7  to  8  feet  of  coal.  The 
quality  of  the  coal  is  intermediate  between  the  semi-bituminous, 
lying  to  the  east  of  it,  and  the  fat  bituminous  coals,  to  the  north  and 
west.  The  Waynesburg  bed,  an  important  seam  in  Greene,  Washing- 
ton, Fayette,  and  Westmoreland  counties;  the  Union  town,  in  Fayette 
and  Greene  counties;  the  Sewickley  and  Redstone  beds,  in  Westmore- 
land and  Allegheny  counties,  are  also  in  the  Upper  Productive  measures. 

The  Lower  Barren  measures  contain  several  workable  beds  of 
limited  area  in  Indiana,  Somerset,  Butler,  Armstrong,  and  Beaver 
counties. 

The  Lower  Productive  measures  contain  the  Freeport  Lower  coal,  a 
bed  of  great  importance  in  Jefferson,  Indiana,  Clearfield,  Cambria, 
Armstrong,  Centre,  and  Allegheny  counties,  and  workable  in  parts  of 
Beaver,  Butler,  Elk,  Blair,  Cameron,  Westmoreland,  and  Fayette 
•counties;  the  Freeport  Upper  coal,  workable  in  fifteen  counties;  the 
Kittanning  Upper,  or  Darlington,  bed,  consisting  partly  of  cannel  and 
partly  of  bituminous  coal,  of  workable  thickness  in  parts  of  Butler, 


COAL-FIELDS  OF  THE   UNITED  STATES. 


59 


Armstrong,  Somerset,  Beaver  (cannel),  Indiana,  Jefferson,  Elk,  and 
Lycoming  counties;  the  Kittanning  Middle,  locally  workable  in  But- 
ler, Lawrence,  Jefferson,  Armstrong,  Elk,  Cameron,  and  Clarion 
counties;  the  Kittanning  Lower,  workable  in  twenty-two  counties,  an 
excellent  coking  coal  along  the  Alleghany  escarpment,  and  in  the 
western  counties  often  a  good  gas-coal;  the  Millerstown  bed,  locally 
workable  in  Butler  County;  the  Clarion  bed,  in  some  of  the  western 
counties,  usually  quite  thin;  and  the  Brookville  bed  "A"  of  the 
Alleghany  escarpment  counties,  often  a  very  sulphurous  coal. 

The  Conglomerate  series  contains  the  Mercer  Upper  and  Lower 
coals,  workable  over  limited  areas  in  Lawrence,  Jefferson,  McKean, 
Elk,  Mercer,  and  Yenango  counties;  the  Quakertown  coal,  work- 
able over  a  small  area  in  Mercer  County;  and  the  Sharon  coal,  good 
but  nearly  exhausted  in  Mercer  County,  and  thin  and  inferior  in  AYar- 
.ren  and  Crawford  counties. 

Analyses  of  Pennsylvania  Bituminous  and  Semi-bituminous  Coals. 
— The  analyses  given  in  the  two  following  tables  are  selected  from 
reports  of  the  Pennsylvania  Geological  Survey  and  from  various  papers 
in  the  Transactions  of  the  American  Institute  of  Mining  Engineers. 
The  figures  of  approximate  heating  value  per  Ib.  of  combustible  are 
interpolated  from  the  table  on  p.  48  showing  the  relation  of  heating 
value  to  the  percentage  of  volatile  matter  in  the  combustible.  For 

PENNSYLVANIA   SEMI-BITUMINOUS   COALS. 


DO 

tl 

fe     « 

c    .    . 

"  -Q  $ 

T3L 

^ 

Q 

^j  «M  2 

c8  "~  3 

County. 

a 

<S 

1 

g|'S 

K&1 

& 

D 

o 

t_* 

45  $>  & 

«•«.§ 

6 

i 

1 

1 

.a 

3 

1 

ill 

PI 

fc 

^ 

E 

02 

> 

-J 

Bradford      

r. 

0.82 

16.95 

69.26 

0.67 

12  29 

19.7 

15,800 

Sullivan               .... 

12 

13.03 

72.74 

0.61 

10.38 

15.2 

15.700 

17 

K65 

20.50 

67.79 

1.26 

8.85 

23.2 

15,750 

LycomiDEr         •     ... 

2 

1.06 

17.53 

72.42 

0.84 

8.15 

19.6 

15,800 

Centre  

1 

0.60 

22.60 

68.71 

2.69 

5.40 

24.7 

15.700 

8 

(0.47 

16.54 

72.85 

1.98 

8.16 

18.5 

15.8CO 

Huntingdon  .   . 

Extremes  of 

•Jo.79 

13.84 

78.46 

0.91 

6.00 

15.0 

15,700 

5 

0.78 

17.38 

76.14 

0.88 

4.81 

18.6 

15,bOO 

Blair*           . 

9 

1.06 

27.27 

60.69 

2.31 

8.66 

31.0 

15,550 

Cambria: 

Lower  bed,  B  

7 

0.74 

21.21 

68.94 

1.98 

7,51 

23.5 

15,750 

Upper  bed,  C.  .  . 

1 

1.14 

17.18 

73.4<J 

1.41 

6  58 

19.0 

15,800 

Clearfield: 

Upper  bed,  C  
Lower  bed,  D  

9 

8 

0.70 
O.HI 

23.94 
21.10 

69.28 
74.08 

1.42 
0.42 

4  62 
3.3(5 

25.7 
22.2 

1R.700 
15,800 

•Somerset        

30 

1.15 

19.77 

67.78 

1.61 

9.67 

22.6 

15,800 

*  According-  to  these  analyses  the  Blair  Co.  coals  should  not  be  included  in  the 
semi-bituminous  class.  They  are  much  higher  in  volatile  matter  than  tl:<?  semi- 
bituminous  coals  of  Cambria  Co.,  which  is  west  of  Blair  Co. 


60 


STEAM-BOILER  ECONOMY. 


the  semi-bituminous  coals  they  are  probably  within  2$  of  being  accu- 
rate; for  the  bituminous  coals  within  4$. 


I         42.6 

•4 

i/Forest    ! 

j  Mercer  •j'T'T-'      "1 

r'Clarioni  ,h_f i._/ 

-s   ,,.6    jJeffersonr' 
Lawrence7  gx       Jf  34.8 

1   43.5  [  Butler  !  \^  ICIearfield 


McA*!an     j  Potter  I     Ti°3a     I   Bradford 


36.8 


19.7 


hr 

i  Greene 

40.8 
L._        '  - 


/"Center^'   /_ 
.  /  /  24.7       ^£* 

I  /  Indiana / ^'^"^-^^^'^     ^ 

7    33.3    ^ambria/     <v' 

/Blair  / 
'   31.0  /  c 


1  ^        /  r\ 

/Bedford'    C--X  =•  N' 

/*° 


JjLL 


FIG.  2.— SEMT-BITUMINOUS  AND  BITUMINOUS  COAL  REGION  OP  PENNSYLVANIA. 
(The  figures  under  the  names  of  the  counties  represent  the  percentage  of  vola« 
tile  matter  of  the  coals  of  each  county,  as  given  in  the  table  of  analyses.) 

The  figures  of  volatile  matter  per  cent  of  combustible  are  entered 
on  the  accompanying  map  under  the  names  of  the  several  counties. 
It  will  be  seen  that  there  is  a  general  tendency  for  the  volatile  matter 
to  increase  towards  the  west  and  north.  Blair  County  seems  to  be  an. 
exception.  The  boundary  line  along  which  the  semi-bituminous  coals; 
grade,  more  or  less  rapidly,  into  the  bituminous,  and  the  location  of 
beds  of  bituminous  coals  within  the  limits  of  the  portion  of  the  field 
which  contains  the  semi-bituminous  coals,  as  far  as  the  author  is  aware,, 
have  not  yet  been  laid  down  on  any  map. 

The  difference  between  the  semi-bituminous  and  the  bituminous 
coals  of  Pennsylvania  is  an  important  one  economically.  The  formor 
have  on  the  average  a  heating  value  per  pound  of  combustible  about 
6  per  cent  higher  than  the  latter,  and  they  also  burn  with  much  less 
smoke  in  ordinary  furnaces. 


COAL-FIELDS  OF  THE   UNITED  STATES. 


61 


PENNSYLVANIA  BITUMINOUS   COALS. 


County. 

1  Number  of 
Samples. 

Water. 

Volatile 
Matter. 

Fixed  Carbon. 

Sulphur. 

In 
< 

Vol.  Matter, 
per  cent  of 
Combustible. 

|^o| 
Illf 

Hal 
< 

•Jefferson         

26 

1.21 

32.53 

60.99 

1.00 

3.76 

34.8 

15,300 

29 

0.98 

29.26 

58.74 

1.73 

9.46 

33.3 

15,400 

?7 

1.14 

82.27 

59.23 

1.50 

5.97 

35  3 

15  200 

13 

0.95 

29.75 

60.47 

1.79 

7.04 

33.0 

15  400 

potter    

8 

1.72 

32.28 

55.32 

1.01 

9.67 

36.8 

15,100 

11 

2.25 

34.49 

46.25 

2.97 

14.02 

42.6 

14,600 

Olarion       ..    

7 

.97 

38.60 

54.15 

1.19 

4.10 

41.6 

14  700 

1 

.18 

42.55 

49.69 

2.00 

4.58 

46.1 

14,000 

Butler   

11 

.91 

39.88 

48.97 

1.97 

7.22 

44.9 

14,200 

Lawrence       .          

14 

.11 

40.45 

52.51 

1.37 

3.25 

43  5 

14  500 

Beaver             .  .      •  

90 

.96 

39.04 

50.20 

2.00 

6.96 

43.7 

14  500 

91 

.16 

37.11 

50.99 

2.06 

8.72 

42.1 

14,700 

17 

1.14 

35.74 

51.75 

1.79 

9.10 

40.8 

14,800 

Youghiogheny  River*.  . 

1.03 
1.26 

36.49 
30.10 

59.05 
59.61 

0.81 
0.78 

2.61 

8.23 

37.9 
33.5 

15,100 
15,400 

The  following  tables  show  the  great  similarity  in  composition  in 
the  coals  of  the  upper  and  lower  coal-measures  in  the  same  geographi- 
cal belt  or  basin.  They  also  show  the  tendency  of  the  volatile  matter 
to  increase  to  the  westward : 

ANALYSES  FROM  THE  UPPER  COAL-MEASURES   (PENNA.)    IN  A  WESTWARD 

ORDER. 


Localities. 

Moisture. 

Vol.  Mat. 

Fixed  Garb. 

Ash. 

Sulphur. 

Anthracite  

..  1.35 

3.45 

89.06 

5.81 

0.30 

Cumberland,  Md  

..  0.89 

15.52 

74.28 

9.29 

0.71 

Salisbury,  Pa  

..  1.66 

22.35 

68.77 

5.96 

1.24 

31.38 

60.30 

7.24 

1.09 

Greensburg,  Pa  

..  1.02 

33.50 

61.34 

3.28 

0.86 

Irwin's,  Pa  

..  1.41 

37.66 

54.44 

5.86 

0.64 

ANALYSES   FROM  THE 

LOWER   COAL-MEASURES  IN  A   WESTWARD 

ORDER. 

Localities. 

Moisture. 

Vol.  Mat. 

Fixed  Garb. 

Ash. 

Sulphur 

Anthracite  

..  1.35 

3.45 

89.06 

5.81 

0.30 

Broad  Top  

..  0.77 

18.18 

73.34 

6.69 

1.02 

..  1.40 

27.23 

61.84 

6.93 

2.60 

Johnstown  

..  1.18 

16.54 

74.46 

5.96 

1.86 

Blairsville  

..  0.92 

24.36 

62.22 

7.69 

4.92 

Armstrong  Co  

0.96 

38.20 

52.03 

5.14 

3.66 

*  The  Youghiogheny  River  is  in  Allegheny,  Westmoreland,  and  Fayette  coun- 
ties. The  coil  mined  along  this  river  is  a  favorite  coal  in  the  Ohio  and  Mississippi 
river  markets. 

f  Connellsville  is  in  Fayette  County.  The  coal  of  this  region  is  chiefly  used  for 
making  coke  for  blast-furnace  and  foundry  purposes. 


62  STEAM-BOILER  ECONOMY. 

Maryland  Semi-bituminous  Coal. — The  Cumberland  coal-field,  in 
Allegany  Co.,  Md.,  is  30  miles  long  and  of  an  average  breadth  of  4-J- 
miles.  Its  northern  end  reaches  into  Pennsylvania  and  its  southern 
extremity  into  West  Virginia.  The  main  bed  is  from  12  to  14  ft. 
thick.  The  coal  is  one  of  the  best  steam-coals  mined  in  the  United 
States.  It  is  jet  black  and  glossy;  is  friable,  and  becomes  pulverized 
in  transportation  and  handling.  There  are  several  other  beds  from  2 
to  6  ft.  in  thickness,  the  whole  series  of  the  Pennsylvania  coal-meas- 
ures being  found  in  the  district. 

Elk  Garden  and  Upper  Potomac  Coal-fields.* 

On  the  extreme  fringe  of  the  great  Appalachian  coal-basin  is  along, 
narrow,  detached  coal-field,  which  is,  in  some  respects,  one  of  the  most 
important  in  the  United  States.  This  field,  about  90  miles  long  by  2£ 
to  16  miles  wide,  extends  from  the  southwest  corner  of  Somerset  County, 
Pa.,  through  Allegany  and  Garrett  counties, Md. ,  Mineral,  Grant,  and 
Tucker  counties,  W.  Va.,  into  Randolph  County,  W.  Va.  In  this 
distance  four  distinct  subdistricts  are  recognized,  the  Wellersburg  in 
Pennsylvania,  the  Cumberland- Georges  Creek  in  Maryland,  and  the 
Elk  Garden  and  the  Upper  Potomac  in  West  Virginia.  It  is  the  nearest 
to  tide-water  of  all  the  bituminous  coal-fields  which  supply  the  great 
coal  markets  of  the  northern  Atlantic  seaboard,  and  its  coal-beds  are 
so  situated  as  to  permit  a  well-nigh  unlimited  increase  of  production 
should  the  trade  of  these  markets  demand  it. 

This  great  coal-field  has  sometimes  been  termed  the  Cumberland 
coal-field,  but  the  name  is  now  more  appropriately  applied  to  a  coal 
(that  of  the  Big  Vein)  which  is  not  mined  throughout  the  entire  dis- 
trict. As  the  district  is  watered  chiefly  by  the  Potomac  River  and  its 
tributaries,  and  as  most  of  the  mining  is  along  the  banks  of  that  stream, 
the  name  "  Potomac  Basin"  has  been  suggested  for  this  entire  coal- 
field; the  distinctive  and  well-known  names  of  the  several  subbasins, 
however,  being  still  retained. 

The  general  course  of  this  basin  is  northeast  and  southwest.  It  is 
hemmed  in  by  the  Alleghany  Front  Mountains  on  the  east  and  the 
Backbone  Mountains  on  the  west.  Its  general  shape  from  Pennsyl- 
vania to  near  the  southern  border  of  Tucker  County,  W.  Va.,  is  that  of 
a  wedge,  very  narrow  in  Pennsylvania,  only  2-J-  miles  wide  at  the  State 

*  Abstract  from  a  paper  by  Joseph  D.  Weeks,  read  before  the  American  Institute 
of  Mining  Engineers,  1894. 


COAL-FIELDS  OF  THE   UNITED  STATES.  63 

line,  and  widening  as  the  mountains  draw  away  from  each  other,  until, 
at  the  point  named  in  Tucker  County,  it  is  some  16  miles  wide. 

The  northern  end  of  this  field  passes  through  the  western  part  of 
Allegany  County  and  a  portion  of  the  eastern  part  of  Garrett  County, 
Maryland,  and  from  it  the  entire  coal  product  of  Maryland  is 
obtained. 

Virginia, — There  are  several  detached  coal-fields  in  the  Mesozoic 
rocks  east  of  the  Alleghany  Mountains.  They  are  described  by  0.  J. 
Heinrich,  in  Trans.  A.  I.  M.  E.,  1878,  vol.  vi.  The  Richmond  basin, 
189  square  miles,  chiefly  in  Powhatan  and  Chesterfield  counties,  west  of 
Richmond,  is  the  most  important.  It  contains  two  workable  beds,  the 
lower  3  to  5  ft.  thick,  and  the  upper  20  to  40  ft.  thick.  The  coal  is 
chiefly  bituminous,  containing  30$  or  upwards  of  volatile  matter  in  the 
combustible,  but  at  Carbon  Hill  semi-bituminous  is  found,  also  "carbo- 
nite  "  or  natural  coke,  corresponding  in  analysis  to  semi-anthracite. 

The  Appalachian  semi-bituminous  coals  are  found  in  the  south- 
western portion  of  the  State,  in  Tazevvell  County,  on  the  West  Virginia 
border,  and  the  bituminous  coals  in  the  southwestern  corner  of  the 
State  near  the  Kentucky  line. 

The  Pocahontas  coal-field  embraces  parts  of  Buchannan,  Dickin- 
son, Lee,  Russell,  Scott,  Tazewell,  and  Wise  counties,  at  the  southern 
edge  of  the  Flat  Top  region,  including  the  Clinch  valley  field,  con- 
taining the  Lower  Productive  measures  of  the  Appalachian  field. 

The  Pocahontas  Flat  Top  coal-measures  are  above  the  water-level,  in 
seams  ranging  from  5  to  13  ft.  in  thickness,  extending  through  an  area 
estimated  to  contain  not  less  than  300  sq.  miles.  Pocahontas  semi- 
bituminous  coal  is  from  the  Lower  coal-measures  and  contains  from 
18  to  20  per  cent  of  volatile  matter.  It  is  mined  in  Tazewell  County, 
Virginia,  and  in  Mercer  and  McDowell  counties,  West  Virginia,  the 
adjoining  counties  to  the  north.  The  veins  dip  to  the  north  and  west, 
and  the  extension  of  the  Ohio  division  of  the  Norfolk  and  Western 
Railroad  north  to  the  Ohio  River  and  the  road  west  to  the  Cumberland 
Mountains  pass  through  the  Middle  and  Upper  measures,  thus  opening 
up  coal  of  greater  volatile  matter,  bituminous,  splint  and  cannel. 

The  development  of  this  now  famous  region  began  in  1881,  but  not 
until  1883  was  any  coal  shipped  out  of  the  country.  In  the  latter  year 
the  Norfolk  and  Western  Railroad  completed  its  New  River  extension, 
and  then  began  the  industry  which  to-day  makes  the  Flat  Top  field  a 
prominent  factor  in  the  coal  production  of  the  United  States. 


^4  STEAM-BOILER  ECONOMY. 

North  Carolina. — Semi-anthracite  is  found  in  two  unimportant 
beds,  18  ins.  thick,  in  the  Dan  Eiver  field,  40  miles  long,  4  to  7  miles 
^ide,  of  which  8  miles  are  in  Virginia.  The  Deep  River  field,  30 
miles  long  by  3  wide,  contains  five  beds,  all  differing  in  character, 
ranging  from  bituminous  coal  to  an  impure  plumbago,  as  shown  by 
the  following  analyses : 

Volatile  Matter.  Fixed  Carbon.  Ash. 

Bituminous,  3ft.  thick...' 32.8  63.8  4 

Semi-bituminous,  1  ft.  thick 23.6  72.6  4 

Anthracite,    3  ft.  thick 6.6  83.8  9.6 

Plumbaginous  slate,  2  ft.  thick 10.4  78 

Plumbago,  4  ft.  thick 18.2  74 

West  Virginia. — Out  of  54  counties  only  6  are  destitute  of  coal. 
The  quality  is  semi-bituminous  in  the  eastern  portion  of  the  coal-bearing 
•district  and  bituminous  in  the  western.  The  first  coal-field  is  the 
Potomac  basin,  an  extension  of  the  Cumberland  semi-bituminous  coal- 
field of  Maryland.  The  Monongahela  basin  embraces  five  beds,  of  which 
the  Pittsburg,  9|  ft.  of  clear  coal,  is  the  most  important.  This  is  a  gas- 
•coal,  and  makes  a  hard  coke,  but  is  high  in  sulphur.  The  New  River 
>coal-field  lies  in  Fayette  and  Raleigh  counties,  bordering  the  New  River 
from  40  miles  from  Quinnimont  to  Kanawha  Falls.  It  contains  both 
semi-bituminous  and  bituminous  steam,  coking  and  gas-coals  of 
excellent  quality.  The  Kanawha  coal-field  lies  along  the  Kanawha 
Hiver  and  its  branches,  below  the  junction  of  the  New  and  Gauley  rivers. 
The  coal  is  bituminous,  and  includes  gas-coals,  cannel  and  hard  splint 
-coal.  It  is  largely  mined  for  shipment  down  the  Ohio  River. 

"WEST  VIRGINIA  ANALYSES,  FROM  PRIME'S  REPORT  OF  THE  CENTENNIAL  EXHIBIT. 

Moisture.   Volatile      ^ixed      gu]phur-      Agh 

Piedmont,  Mineral  Co 0.82  19.36  75.86  0.71  3.96 

Austen,  Preston  Co 0.11  31.12  66.29  0.64  2.48 

Kingwood,  top  of  bed 0.34  31.47  65.66  0.58  2.53 

Monongahela  Co.,  Upper  Freeport  bed..  0.63  28.06  54.28  0.77  17.03 

"      Pittsburg  bed 0.39  38.64  54.77  2:54  6.20 

"      Redstone  seain 0.37  37.88  54.36  2.87  7.39 

"      Sewickley  seam 0.44  35.78  54.31  3.10  9.47 

11      Way nesburg  seam...  0.74  35.36  56.35  0.71  7.55 

Despard,  Harrison  Co 40.00  53.30  . . .  6.70 

Murphy's  Run,  Harrison  Co 1.58  37.10  49.08  2.84  940 

Wood's  Run,  Ohio  Co 1.74  42.97  50.99  2.88  4.30 

Hartford,  Putnam  Co 3.43  44.38  46.88  1.57  5.30 

Osborn,  Wayne  Co 2.30  40.43  48.72  0.76  8.55 

CANNEL-COAL. 

Falling  Rock  Creek,  Elk  River 43.20        50.80        ....         6.00 

Peytona,  Boone  Co 46.00        41.00        ....       13.00 


COAL-FIELDS  OF  THE   UNITED  STATES. 


65 


ANALYSIS   OF   WEST   VIRGINIA   COALS,  NEW   RIVER   REGION. 
Moisture. 

Quinnimont  lump 0.76 

"  slack 0.83 

Fire  Creek 0.61 

Longdale  (Sewell) 1.03 

Nuttalburg ...  1.35 

Hawk's  Nest 0.93 

Ansted 1.40 

Eastern  Kentucky. — The  Appalachian  field  extends  into  Eastern 
Kentucky,  including  fifteen  counties  and  portions  of  five  others,  cov- 
ering altogether  8983  square  miles.  The  following  analyses  are  from 
Owen's  Geological  Survey  of  the  State: 


Volatile 
Matter. 

Fixed 
Carbon. 

Sulphur. 

Ash. 

18.65 

79.26 

0.23 

1.11 

17.57 

79.40 

0.28 

1.92 

22.34 

75.02 

0.56 

1.47 

21.38 

72.32 

0.27 

5.27 

25.35 

70.67 

0.57 

2.10 

21.83 

75.37 

0.26 

1.87 

32.61 

63.10 

0.74 

2.15 

No.  of 
Bed. 

1. 


Locality.  Moisture. 

Lawrence  County 3. 50 

Carter  County 4. 10 

Greenup  County 3.56 


Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

36.30 

57.30 

2.90 

1.15 

34.60 

55.25 

4.77 

1.41 

35.00 

52.34 

y.02 

2.59 

66.30 

28.30 

4.80 

1,32 

32.30 

53.00 

11.50 

1.20 

33.77 

54.51 

8.91 

1.56 

32.04 

55.59 

6.71 

1.68 

4.  Carter  County  (cannel) 0.60 

5.  Lawrence  County 3. 20 

6.  Boyd  County 3.27 

7.  Coalton  County 5.19 

The  following  analyses  of  Eastern  Kentucky  coals  are  taken  from 
a  report  by  Capt.  H.  S.  Hodges,  Corps  of  Engineers  U.  S.  A.,  January, 
1900,*  on  a  Survey  of  the  Big  Sandy  Eiver,  West  Virginia  and  Ken- 
tucky, including  Levisa  and  Tug  Forks : 


LAWRENCE  COUNTY: 


No.  of 
An- 
alyses. 


Moist- 
ure. 


Volatile 
Matter. 


Fixed 
Carbon. 


Ash. 


Vol.  Mat. 

Sulphur.  %  of  Com- 
bustible. 


Peach  Orchard  coal 

2 

4.60 

35.70 

53.28 

6.42 

1.08 

40.1 

McHenry  coal  

1 

(3.24 
)3.36 

36.56 
37.05 

54.95 

52.82 

5.24 
5.55 

1.19 
1.22 

40.0 
41.2 

JOHNSON  COUNTY: 

Bituminous  coals.  . 

5 

(  2.66 
(  1.20 

38.04 
41.80 

56.30 
46.00 

3.00 
11.00 

1.29 
0.96 

40.3 
47.6 

Cannel  coals      .... 

8 

t  1.80 

49.20 

44.00 

5.00 

0.85 

52.8 

U.20 

64.39 

26.36 

8.05 

1.67 

71.0 

FLOYD  COUNTY: 

(3.80 

33.80 

60.60 

1.80 

0.48 

35.8 

9 

(  1.30 

36.70 

51.70 

10.30 

1.36 

41.5 

PIKE  COUNTY: 

37 

ii.so 

26.80 

67.60 

3.80 

0.97 

28.4 

(1.60 

41.00 

50.37 

7.00 

0.03 

42.9 

Average  of 

37 

... 

34.77 

58.61 

.... 

.... 

37.2 

Cannel  coal  

1 

0.58 

54.07 

40.64 

4.70 

0.87 

57.1 

MARTIN  COUNTY: 

3 

<  1.46 

32.60 

62.68 

3.26 

34.2 

(2.47 

34.18 

55.03 

8.32 

1.17 

38.3 

*  H.  R.  Document  No.  326,  56th  Congress,  1st  Session. 


66 


STEAM-BOILER  ECONOMY. 


The  analyses  here  given  are  selected  from  those  in  the  original 

report,  to  show  the  range  of  quality,  as  indicated  by  the  percentage  of 

volatile  matter  in  the  combustible,  of  the  coals  of  the  several  counties* 

-  The  relative  location  of  the 

counties,  and  the  percentage  of 
volatile  matter  per  pound  of 
combustible  in  the  bituminous 
(not  cannel)coal  in  each  county, 
as  given  in  the  table,  are  shown 
in  the  accompanying  map. 

The  author  commends  to- 
State  geologists  and  others- 
•who  have*  occasion  to  make  re- 
ports on  the  extent  and  quality 
of  coal  deposits  the  method  of 
mapping  both  the  location  and 
the  quality  which  is  shown 
here  and  also  on  pages  60  and 
72.  The  reports  of  the  U.  S. 
Geological  Survey,  of  the  U.  S. 
Census,  and  of  the  Geological 
Surveys  of  the  several  States 
would  be  of  greater  value  than 

FIG.  3.— BTG  SANDY  COAL  REGION  OP      they    now    are    if    they    con- 
EASTERN  KENTUCKY.  tajned  guch  maps 

Tennessee. — The  Appalachian  field  crosses  the  eastern  part  of 
Tennessee  in  a  comparatively  narrow  belt,  71  miles  wide  at  the  north- 
ern boundary  and  narrowing  to  50  miles  at  the  southern  or  Ala« 
bama  and  Georgia  State  line.  The  workable  coal-area  is  confined  to 
what  is  known  as  the  Cumberland  table-land.  About  5100  square 
miles  are  contained  in  the  area,  which  is  embraced  in  nineteen  conn- 
ties.  There  are  nine  seams,  of  which  six  are  over  3  ft.  in  thickness. 
The  coals  range  from  semi-bituminous  to  bituminous,  and  some  are  of 
excellent  quality.  In  Campbell  County  is  a  part  of  the  famous  Jellica 
steam-coal  field.  The  Sewanee  vein  is  one  of  the  most  important  ones 
in  the  State  and  is  worked  extensively  in  Grundy  County.  Coke  of 
high  grade  is  made  from  the  coal  of  this  seam.  A  comprehensive 
paper  on  the  Tennessee  coal-fields,  by  Prof.  J.  M.  Safford,  was  pub- 
lished in  "  Mineral  Resources,"  1892. 


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I      A 


COAL-FIELDS  OF  THE   UNITED  STATES. 


67 


ANALYSES  OF  TENNESSEE  COALS. 

Moisture  and  Fixed 

Volatile  Matter.       Carbon.  Asn> 

Addison's  Creek,  Cumberland  Mountains.  9.00  83.22  7.78 

Crow  Creek 14.00  77.70  8.30 

Sewanee  Mining  Co 14.21  79.56  6.25 

Tracy  City 29.00  65.50  5.50 

Marion,  Upper  Seam 38.00  59.50  2.50 

Etna 21.39  74.20  441 

Chattanooga 26.80  63.90  9.30 

Coal  Creek,  Anderson. 40.00  55.00  5.00 

Georgia. — The  Appalachian  coal-field  enters  the  extreme  northwest 
corner  of  the  State,  the  coal-measures  occupying  an  area  of  from  150 
to  170  sq.  miles.  The  coal  is  similar  in  quality  to  that  of  Tennessee. 
One  analysis,  from  Dade  Co.,  gave:  Moisture,  1*20;  volatile  matter, 
23.05;  fixed  carbon,  60.50;  ash,  15.16;  sulphur,  0.84. 

Alabama. — The  southern  extremity  of  the  Appalachian  coal-field 
covers  about  5500  sq.  miles,  in  the  northern  part  of  the  State.  There 
are  three  separate  basins :  the  Warrior,  5000  sq.  miles,  extending  nearly 
across  the  State;  the  Cahaba,  180  to  200  sq.  miles,  to  the  southwest  of 
the  Warrior  field,  and  the  Coosa,  150  sq.  miles,  east  of  the  Cahaba  and 
on  the  northwest  side  of  the  Coosa  Eiver.  The  coal-measures  contain 
ten  or  twelve  beds  of  workable  thickness.  The  Cahaba  Basin  coals  are 
the  best  in  the  State.  The  larger  bed  is  12  ft.  thick,  of  good  coal. 

The  following  analyses  are  from  the  reports  of  E.  A.  Smith,  State 
geologist : 

Bed.  County.  Moisture. 

Cahaba  Basin : 

Cahaba Shelly 1.66 

McGinnis 1.91 

Moyle 1.93 

Little  Pittsburg 2.05 

Conglomerate 2.13 

Helena 2.54 

Montevallo , 2.13 

"Warrior  Basin  : 

Townley Walker 3.01 

Jagger "      3.09 

Burnett's Marion 3.69 

Pratt  Co.'s Upper  Jefferson..  1.47 

Lower        "  1.53 


Sulphur. 

.53 
.63 

3.78 
.64 

1.48 
.53 
.50 

.71 

.57 
1.73 
1.22 

.61 

Ohio. — The  Appalachian  coal-field  in  Ohio  covers  more  than 
10,000  square  miles  in  the  eastern  and  southeastern  portion  of  the 
State,  its  length  being  about  180  miles  and  its  width  about  80  miles. 
The  coals  are  all  of  the  bituminous  variety,  are  known  in  general 
terms  as  block  coal,  gas-coal,  cannel-coal,  etc.,  and  by  many  special 
names,  as  Mahoning  Valley,  Hocking  Valley,  Salineville,  etc.,  accord- 


Volatile 

Fixed 

Matter. 

Carbon. 

Ash. 

33.28 

63.04 

2.02 

32.65 

63.91 

1.53 

32.84 

59.64 

5.59 

33.47 

62.20 

2.28 

30.86 

64.54 

2.47 

29.44 

66.81 

1.21 

27.03 

66.22 

4.62 

29.08 

63.35 

4.56 

29.04 

56.54 

11.33 

35.38 

58.52 

2.41 

32.29 

59.50 

6.73 

30.68 

63.69 

4.10 

68  STEAM-BOILER  ECONOMY. 

ing  to  the  producing  localities.  Thirteen  workable  beds  are  found 
along  the  Ohio  Kiver,  but  only  two  of  them,  No.  6,  or  the  '•'  Great 
Vein"  of  Perry  Co.,  and  No.  8,  or  the  Pittsburg  bed,  are  found  work- 
able over  great  areas.  No.  1,  the  "  block  coal"  of  the  Mahoning  Val- 
ley, called  elsewhere  "Massillon"  and  "Jackson"  coal,  is  of  great 
excellence  wherever  found.  It  is  thinly  laminated,  and  is  broken  by 
transverse  cleavages  into  cubical  blocks,  whence  its  name  of  "block 
coal." 

ANALYSES  OF  OHIO  COALS   FROM   DIFFERENT  BEDS  (NEWBERRY). 

Coal,  No.              Locality.            Moisture.  Vol.  Mat.  Fixed  Garb.  Ash.  Sulphur^ 

I.  Mahoning  Co 2.47  31.83  64.25  1.45  0.56  * 

II.  Holmes  Co 2.15  28.65  52.70  16.50  2.13 

III.             "          3.90  40.50  49.95  5.65  1.55 

III.  Yellow  Creek 2.50  36.60  56.30  4.60  2.05 

IV.  CoshoctonCo.(Cannel)1.50  44.40  44.50  9.60  1.72 
IV.  Stark  Co 7.00  30.80  59.50  2.70  0.65 

V.     Columbiana  Co 1.15  40.45  53.75  4.65  3.51 

VI- .  "  1.60  29.29  64.50  4.00  2.80 

VI.     Muskingum  Co 3.47  37.88  53.30  5.35  2.24 

VI.     Jefferson  Co 1.40  30.90  65.90  1.80  0.98 

VII.     Saline  Co 1.70  34.30  59.50  4.50  1.63 

VII.     Carroll  Co 2.80  30.20  6410  2.90  1.23 

VIII.     Harrison  Co 2.44  32.36  59.92  5.28  2.62 

The  following  are  average  figures  for  some  Ohio  coals  by  Lord  and 
Haas.  See  Chapter  V,  on  "  Heating  Value  of  Coal." 

Upper  Freeport  Bed 1.93  37.35  51.63  9.10  2.89 

Middle  Kittanning  Bed  (Hock- 
ing Valley) 6.59  35.77  49.64  8.00  1.59 

Jackson  Co 8.17  35.79  52.78  3.25  1.13 

THE   NORTHERN    OR   MICHIGAN    COAL-FIELD. 

The  coal  deposits  of  Michigan  are  detached  from  those  of  any  other 
State,  and  form  what  is  known  as  the  Northern  field.  The  area  is 
about  6700  square  miles,  the  central  point  being  near  the  town  of  St. 
Louis,  in  Gratiot  County,  and  the  southern  boundary  passing  a  few 
miles  south  of  Jackson,  in  Jackson  County.  Beyond  this  to  the  south 
there  are  several  detached  patches  of  productive  coal-measures.  The 
greatest  thickness  of  the  measures  is  found  along  a  line  extending  from 
Ionia  County  to  Saginaw,  the  thickest  coal-beds  lying  along  Six  Mile 
Creek.  There  is  one  seam  of  bituminous  coal,  3  or  4  ft.  thick,  and 
toward  the  centre  of  the  basin  there  are  several  other  beds.  One 
analysis  gives :  Moisture,  2 ;  volatile  matter,  49 ;  fixed  carbon,  45 ;  ash, 
2;  sulphur,  2.  The  principal  operations  are  carried  on  near  the  city 
of  Jackson,  in  Jackson  County,  but  these  are  small  when  compared 
with  other  States. 


COAL-FIELDS  OF  THE  UNITED  STATES.  69 

The  Michigan  coals  are  of  inferior  quality  when  compared  to  those 
shipped  by  lake  and  rail  into  the  State,  and  the  imported  coals  are 
sold  so  cheap  that  there  is  little  encouragement  for  the  development  of 
the  Michigan  field. 

THE   ILLINOIS   COAL-BASIN. 
(Indiana,  Illinois,  and  Western  Kentucky.) 

Indiana.  —  The  Illinois  coal-field  extends  into  the  western  part  of 
Indiana,  covering  an  area  of  6500  square  miles.  The  following  analyses 
are  given  by  the  State  Geological  Survey: 

ANALYSES   OF   INDIANA   COALS. 

Moisture.  Volatile  Matter.  Fixed  Carbon.  Ash. 
Caking  coals. 

Parke  Co  ...............     4.50  45.50  45.50  4.50 

Sullivan  Co.  coal  M  .....     2.35  45.25  51.60  0.80 

Clay  Co  ................     7.00  39.70  47.30  6.00 

Spencer  Co.,  coal  L  .....     3.50  45.00  46.00  2.50 

Block  coals. 

Clay  Co  ................  8.50  31.00  57.50  3.00 

Martin  Co  ..............  2.50  44.75  51.25  1.50 

Daviess  Co  .............  5.50  36.00  53.50  5.00 

The  following  ultimate  and  proximate  analyses,  credited  to  Noyes, 
McTaggart,  and  Craven,  are  taken  from  Poolers  "  Calorific  Power  of 
Fuels  "  : 

T        i-f  n    K       Hydro-     Oxy-       Nitro-     Sul-        Wnt-oi.       A^VI      Fixed       Vol. 

Locality.          Carbon.     ^        ge£         gen       phur        Water.     Ash.     Carb      Matter> 

Brazil  ..........  70.50  4.76  16.29  1.36  1.39  8.98  6.28  50.30  34.49 

Lancaster  ......  71.41  5.56  18.42  1.54  0.62  12.66  2.68  47.22  37.64 

New  Pittsburg..  62.88  5.07  1306  1.01  7.46  6.83  13.30  39.93  39.92 

'•'  65.26  5.17  13.25  1.17  5.88  5.89  11.48  40.40  42.23 

Shelburn  .......  66.86  530  15.69  1.50  2.57  8.63  9.05  43.45  38.82 

Western  Kentucky.  —  The  Illinois  coal-field  extends  into  the  north- 
western portion  of  the  State,  including  ten  counties  and  portions  of 
five  others,  having  an  area  of  3888  square  miles  of  coal-measures.  There 
are,  in  places,  twelve  beds,  but  the  number  varies  with  the  locality. 
The  following  analyses  are  from  Prime's  Centennial  Keport  on  Coal  : 


Moisture.  Carbon.  Ash'  Sulphur 

Coal  A  (average)  ..  .........  4.15  33.14  55.71  7.00  1.87 

««    B(average)  .............  3.65  38.40  51.87  6.06  3.12 

«'    C  (gas-coal  layer)  .......  4.60  40.10  51.35  3.95  1.49 

••    D  (average)  _____  .......  3.82  35.41  52.11  8.41  3.33 

"    J  (Christian  Co.)  .......  3.70  32.56  50.04  13.70  3.72 

"    L  (average)  ............  4.23  33.21  54.19  8.35  1.50 

Breckenrid™  cancel  .......  1.44  G2.10.  2820  7.96  2.44 


70 


STEAM-BOILER  ECONOMY. 


No.  of 
Samples. 

Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Nolin  River  District 

a 

1 

3.40 
to  4.70 

to 

30.66 
33.24 

to 

51.70 
54.94 

Muhlenberg  Co  

7 

! 

3.60 
to  7.06 

to 

30.60 
38.70 

to 

50.50 

58.80 

Hancock  Co  ........ 

7 

1 

3.30 
to  7.46 

33.14 
to  43.40 

to 

45.56 
55.20 

Ohio  Co  

5 

1 

3.70 
to  5.30 

to 

30.70 
45.70 

to 

45.00 
55.30 

Breckenridge  Cannel 

4 

i 

0.64 
to  1.44 

to 

54.40 
62.40 

to 

27.00 
32.00 

The  following  are  from  the  Geological  Survey  of  Kentucky,  1884, 
Western  Coal-Field,  D. : 

.    .  "\7rtlttfrilA  T7*;,,^,i 

Ash.  Sulphur. 

11.06  1.95 

to  11. 70  to  2. 54 

3.40  0.79 

to  9.20  to  4. 57 

4.20  1.32 

to  11.00  to  4. 04 

3.16  1.24 

to  14.20  to  3. 13 

7.96 

•to  12.30  1.89 

The  Nolin  River  district  embraces,  portions  of  Grayson,  Edmonson, 
Hart,  and  Butler  counties. 

Illinois. — The  coal-field  of  Illinois  occupies  an  area  of  36,800 
square  miles,  or  nearly  two-thirds  of  the  area  of  the  State.  The  coal- 
measures  contain  six  beds  of  workable  size,  with  a  total  thickness  of 
24  ft.,  but  the  beds  are  irregular,  often  wanting,  and  often  containing 
an  inferior  quality  of  coal.  In  the  DuQuoin  district,  Perry  Co.,  two 
seams,  V  and  VI,  6  to  7  ft.  thick,  are  worked  within  75  ft.  of  the 
surface.  In  the  Big  Muddy  district,  Jackson  Co.,  the  coal  occurs  near 
the  surface.  The  lower  seams  produce  a  good  block  coal.  From  the 
Belleville  district,  St.  Clair  Co.,  St.  Louis  obtains  most  of  its  bitumin- 
ous coal.  Coal  seam  VI,  5  to  7  ft.  thick,  is  principally  worked.  The 
lower  seams  contain  more  sulphur  and  the  quality  varies.  Other  large 
producing  districts  are  at  Neelysville,  Danville,  and  La  Salle.  The  lat- 
ter is  of  importance  from  its  proximity  to  Chicago.  There  are  three 
workable  beds,  VI,  4£  to  5  ft.;  V,  3  to  9  ft.,  usually  6  ft.;  II,  4  ft. 
The  coal  of  the  upper  bed,  No.  VI,  is  light,  dry,  and  free-burning. 
No.  V  is  a  purer  coal.  No.  II  is  most  highly  bituminous,  cakes  in 
burning,  is  high  in  sulphur,  and  throws  off  heavy  soot.  In  the  Wil- 
mington district,  Will  Co.,  there  is  a  workable  seam  of  coal  which  is 
largely  used  for  household  and  steam  purposes.  The  Illinois  coals  are 
generally  high  in  moisture,  and  are  often  very  high  in  sulphur  and 
ash.  When  burned  in  ordinary  furnaces  they  produce  great  volumes 
of  black  smoke. 

Notes  to  the  Table  of  Analyses  of  Illinois  Coals. — The  sources  of 
information  from  which  these  analyses  were  obtained  are  the  follow- 
ing, referring  to  the  figures  prefixed  to  the  names  of  the  towns: 
1.  Proceedings  Engineers'  Club  of  St.  Louis,  as  given  in  Wickes 


COAL-FIELDS  OF  THE   UNITED  STATES.  71 

Bros.'  catalogue.  2.  D.  L.  Barnes,  Trans.  A.  S.  C.  E.,  1893.  3,  4. 
Catalogue  of  Wickes  Bros.,  credited  respectively  to  McConney  and 
Forsyth.  5.  Analyses  and  calorimetric  determinations  (by  the  Car- 
penter calorimeter)  made  for  the  author  by  C.  W.  Hough  ton,  M.E., 
at  Cornell  University  in  1896.  6.  William  II.  Bryan,  Engineers' 
Club  of  St.  Louis,  1896,  average  of  four  analyses.  7.  Analysis  of 
Staunton  coal  made  for  the  author  by  the  Pittsburg  Testing  Labora- 
tory in  1883  (Trans.  A.  S.  M.  E.,  vol.  iv,  p.  256).  This  particular 
coal  gave  the  lowest  result  the  author  has  ever  obtained  in  a  boiler 
test,  viz.,  5.09  Ibs.  of  water  evaporated  from  and  at  212°  per  Ib.  of 
coal,  and  6.7  Ibs.  per  Ib.  of  dry  combustible,  the  ash  and  refuse  ob- 
tained in  the  test  being  17.7$,  and  the  moisture  in  the  coal,  by  analy- 
sis, 6.3$.  The  boiler  in  this  case,  having  3358  sq.  ft.  of  heating  sur- 
face, and  rated  at  292  11. P.,  developed  only  246  H.P.,  with  a  grate- 
surface  of  60  sq.  ft.  and  a  good  draft,  burning  25.1  Ibs.  of  coal  per 
sq.  ft.  of  grate  per  hour;  while  with  Jackson  Co.,  Ohio,  coal,  the 
same  boiler,  with  the  grate-surface  cut  down  to  48  sq.  ft.,  and  burning 
•only  17.7  Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour,  developed  460 
H.P. ,  or  over  57$  above  rating,  with  an  evaporation  from  and  at 
212°  of  8.93  Ibs.  per  Ib.  of  coal  and  9.88  Ibs.  per  Ib.  of  combustible, 
not  corrected  for  moisture  in  the  coal.  The  analysis  of  this  Staunton 
coal  shows  a  far  higher  percentage  of  volatile  matter  in  the  com- 
bustible (68.5$)  than  any  other  of  the  Illinois  coals  thus  far  reported, 
and  nearly  the  same  as  that  shown  by  the  Breckenridge  cannel-coal 
of  Kentucky.  During  the  boiler  test  the  coal  gave  off  dense  volumes 
of  jet-black  smoke  for  a  minute  or  two  after  each  firing.  The  fur- 
nace was  evidently  not  adapted  for  burning  this  kind  of  coal. 

Another  analysis  of  Staunton  coal  is  given  in  Poole's  "  Calorific 
Power  of  Fuels,"  credited  to  Prof.  Carpenter,  as  follows:  Dry  coal, 
volatile  matter,  36.0;  fixed  carbon,  48.0;  ash,  16.0;  volatile  matter 
per  cent  of  combustible,  42.  9.  This  is  very  different  from  the  highly 
volatile  coal  mentioned  above,  and  is  practically  identical  with  the 
Mt.  Olive  coal  from  the  same  county. 

An  analysis  of  Collinsville,  Madison  Co.,  coal,  forty  miles  south  of 
Staunton,  found  in  Wickes  Bros/  catalogue,  credited  to  Engineers* 
•Club  of  St.  Louis,  but  not  included  in  the  table,  is:  Water,  5.3; 
volatile  matter,  43.9;  fixed  carbon,  31.6;  ash,  9.2;  volatile  matter 
per  cent  of  combustible,  58.1.  This  analysis  approaches  that  of  the 
volatile  Staunton  coal  and  differs  greatly  from  the  analysis  of  Collins- 
ville coal  given  in  the  table. 


72 


STEAM-BOILER  ECONOMY. 


— -I 
i  Me  Lean  j 

r-i.r._4^_.J, 

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or,-        hL43-8  1— — \ 
rlZfir1-!.       jMawn 

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FIG.  4.— RELATIVE  POSITION  OF  THE  COUNTIES 
OP  ILLINOIS  NAMED  IN  THE  TABLE  OF  ANALY- 
SES OF  ILLINOIS  COALS. 


NOTE   TO    THE   MAP. 

The  accom pan}7 ing- 
skeleton  map  shows  the- 
relative  locations  of  the 
counties  of  Illinois  men- 
tioned in  the  table,  with 
the  average  percentage  of 
volatile  matter  in  the 
combustible  of  the  coal  in 
each  county.  The  highly 
volatile  Staunton  coal  is 
not  included  in  the  aver- 
age of  Macoupin  Co. 

It  will  be  noted  that 
the  coals  in  the  southern 
part  of  the  State  are  much 
lower  in  volatile  matter 
than  those  in  the  central 
and  northern  parts.  The 
author  will  be  glad  to  fill 
up  the  blank  spaces  in 
this  map  in  future  edi- 
tions of  this  work  if  he  is 
furnished  with  the  neces- 
sary data. 


ANALYSES   OF   ILLINOIS   COALS. 


County. 

Town  or  District. 

Moisture. 

Volatile  Matter. 

1 

s 

1 

I 

"3 

02 

-2           ® 

sri        P 

Heating;  Value 
per  pound 
Combustible, 
B.T.U, 

11  6 
120 
85 
100 
72 
13.3 
2.4 
3.5 
3.2 

25.0 
32.3 
335 
33.8 
36.4 
30.4 
32.9 
37.0 
32.9 

44.8 
42.5 
44.1 
40.9 
46.9 
52.0 
42.6 
46.7 
43.1 

18.6 
13.2 
13.8 

9^5 
4.3 
22.0 
12.8 
20  8 

"09 

35.8 
43.2 
43.2 
45.3 
43.7 
37.0 
43.6 
44.2 
43.H 

14,700 

Christian  
Clinton  

*  Ladd  

4      «( 

6  Seatonville  

8Pana  

1  Trenton  
4  Bryant  

Fulton  

«  Claire  

COAL-FIELDS  OF  THE   UNITED  STATES. 
ANALYSES   OF  ILLINOIS   COALS— Continued. 


County. 

Town  or  District. 

Moisture. 

Volatile  Matter. 

Fixed  Carbon. 

•a 

•— 

3 
,4 

a 
£ 

Volatile  Matter, 
per  cent  of 
Combustible. 

§      « 

sj-3 

^s'i 

i&id 
IilS 

Fulton  

4  Cuba     

4  2 

36.4 

48  6 

10  8 

42  8 

2  5 

32  9 

45  6 

19.1 

43  2 

4  Farmington  
4  St.  David  

3.4 

2.0 
7.1 

33.9 
34.6 
32  1 

45.9 
46.2 

49  7 

16.8 
17.2 
11.1 

425 
42.8 
39  2 

Jackson.  ... 

1  Big  Muddy             .... 

6  4 

30  6 

54  6 

8  3 

1  5 

35  9 

7  7 

31  9 

53  0 

7  4 

37  6 

U55(V 

6  4 

26.4 

59.8 

7  4 

30  6 

La  Salle  .... 

«  Mt.  Carbon  
2  La  Salle  

6.1 
8  2 

24.7 
39  4 

66.5 
44  0 

2.7 

8  4 

.... 

27.1 

43  8 

»  Peru  

6.6 

37.2 

47  2 

9  0 

44  1 

1  Streator  

2             <« 

12.0 
7  2 

35.3 
38  9 

48.8 
45  3 

3.9 

8  6 

2.4 

42.0 

46  2 

6              «          J, 

9  9 

33  2 

42  2 

14  6 

44'  o 

14  200> 

Logan  

8.4 

35  0 

44  5 

12  1 

44  0 

3  Mt.  Pulaski  

7.7 

35.8 

46.5 

10.0 

43  5 

3  Niantic  

7  9 

36.3 

47.4 

8  5 

42  9 

Macoupin  .... 

1  Gillespie  

12  6 

30  6 

4=)  3 

11  5 

1  5 

40  3 

1  Girard  

9  7 

34  4 

45  8 

10.1 

3  5 

42  9 

i  Mt   Olive 

10  4 

36  7 

40  1 

6  8 

3  5 

44  3 

e    «      >< 

8.1 
6,3 

33.1 
57  1 

44.1 
26  3 

14.7 
10  3 

42.9 
68  5 

13,70ft 

Madison.  .    .  . 

6Collinsville  

9  3 

29.9 

40  8 

16.1 

3.9 

42  2 

Marion  

3  Centralia  

8  3 

34.0 

45.5 

80 

42  8 

s  Odin  

6  1 

34  0 

50  9 

9  1 

40  0 

3  Bloomington  

4.1 

36.4 

45  2 

14  7 

44  6 

Peoria  

4  Edwards  

1  9 

34.5 

43  6 

20  0 

44  2 

4  Elmwood  
4  Peoria  

1.4 

3.2 
4  6 

27.7 
36.1 
35  5 

35.4 
49.2 
45  5 

35.5 
11.4 
14  4 

43.9 
42.3 

43  8 

Perry  

11.3 

30.3 

49  9 

8.5 

0.9 

37  8 

2     «<          «< 

1  St.  John..'  .........!!! 

8.9 
13.6 

23.5 
24.5 

60.6 
43  5 

7.0 
15  4 

'  1  8 

28.0 
36  0 

Sangainon  .  .  .  . 
St   Clair,  .  .  . 

1  Barclay  

3           •' 

1  Loose's  
8  Riverton  
1  Heintz  Bluff 

10.8 
7.4 
10.7 
6.4 
9  0 

27.3 
35.7 
37.6 
35.4 

37  8 

44.8 
46.2 
45.1 

48.4 
48  2 

17.1 
10.7 
6.6 
9.8 
5  0 

'  V.4 
33 

37.9 
43.6 
45.5 
42.2 
43  9 

1  Oakland  
1  St.  Bernard  

8.3 
14.4 
10  3 

34.4 
30.9 

27  9 

43.1 

48.4 
49  0 

14.2 
6.4 
12  8 

4.4 
1.4 
0.7 

44.4 
38.8 
36  3 

"Vermilion  .... 

2  Danville     

11  0 

32  6 

53  0 

3  6 

38  0 

3             « 

«         « 

4.8 
5  6 

43.r< 
37  1 

45.4 
46.4 

5.2 
10  9 



49.1 
44  3 

Will  

s  "Wilmington  Lump 

15  5 

32  8 

39  9 

11  8 

45  1 

14  050> 

*         "              Screenigs.. 
5        "  washed      " 

14.0 
14.5 

28.0 
29.5 

34.2 
42.9 

23.8 
13.1 

.... 

45.0 
40.7 

13,200- 
14,200 

*  Average  of  two  samples. 


t  Average  of  five  samples. 


'74  STEAM-BOILER  ECONOMY. 

The  heating  values  of  Illinois  coals  published  in  Poole's  "  Calorific 
Power  of  Fuels"  and  other  works  were  determined  mostly  by  the 
Thompson  calorimeter.  They  are  not  considered  reliable  and  have 
therefore  been  omitted  from  the  table. 


THE   MISSOURI    COAL-BASIN. 

"(Iowa,  southeastern  Nebraska,  Missouri,  eastern  Kansas,  Arkansas,  Indian  Terri- 

tory,  Texas.) 

The  separation  of  the  Western  coal-field,  of  which  Missouri  forms 
an  important  part,  from  the  Illinois  or  Central  field  is  made  by  the 
Mississippi  River  and  its  immediate  valley.  At  one  place  near  the 
northern  border  of  the  Illinois  field  the  present  course  of  the  Missis- 
sippi cuts  through  it,  a  small  portion  of  the  Central  field  being  found 
across  the  river  in  Iowa.  The  two  fields  are  really  the  same,  the 
barren  valley  being  a  narrow  one,  and  in  it  isolated  bodies  of  coal  are 
found  both  in  Iowa  and  Missouri.  It  has  been  customary,  however, 
to  consider  them  separately. 

Iowa. — The  Missouri  coal-basin  occupies  nearly  one-half  of  the 
State.  The  coal-measures  are  divided  into  upper,  middle,  and  lower, 
the  latter  of  which  contains  the  productive  seams,  two  in  number. 
They  are  of  irregular  thickness,  sometimes  reaching  5  ft.  An  average 
of  64  analyses  made  by  the  State  geologist  gives:  Moisture,  8.57;  Vol- 
atile matter,  39.24;  Fixed  carbon,  45.42;  Ash,  6.77. 

Four  analyses  by  Forsyth,  given  below,  show  a  wide  range  of 
quality : 

Volatile  Volatile  Matter, 

Locality.  Water.  Matter         Fixed  Carbon.  Ash.  per  cent  of 

tei-  Combustible. 

Cliisolm 9.18  40.42  39.58  10.82  50.5 

Flagler's 9.48  40.16  37.69  12.31  51.6 

Hiteman 4.99  35.27  25.37  34.37  58.0 

Keb 9.81  37.49  44.75  7.95  45.6 

The  coal  from  Hiteman  appears  to  be  a  cannel-coal  very  high  in 
ash. 

Missouri. — The  coal-measures  are  contained  chiefly  in  the  northern 
and  western  portions  of  the  State.  An  arm  of  this  territory,  however, 
follows  the  course  of  the  Missouri  River  eastward  for  a  short  distance 
in  the  central  part  of  the  State,  and  some  coal  is  also  found  in  the 
vicinity  of  St.  Louis.  The  total  area  included  is  estimated  at  about 
"25,000  square  miles,  distributed  over  fifty-seven  counties  in  whole  or 


COAL-FIELDS  OF  THE   UNITED  STATES.  Y5 

in  part.  All  of  the  coals  are  of  the  bituminous  variety,  with  the  ex- 
ception of  some  limited  deposits  which  approach  cannel-coal  in  char- 
acter. The  bituminous  coals  have,  as  a  rule,  a  high  percentage  of  ash 
compared  with  the  best  coals  of  this  character.  They  are  compara- 
tively soft,  and  deteriorate  by  exposure  or  much  handling.  They  also 
usually  carry  considerable  sulphur  in  the  form  of  pyrite. 

There  are  16  seams  in  three  measures,  of  which  seven  are  of  work- 
able thickness.     Analyses,  by  C.  G.  Brodhead,  are  as  follows: 

ANALYSES   OF    MISSOURI   COALS. 


County. 
Ray.. 

Moisture. 
10  05 

Volatile 
Matter. 

38.55 
33.10 
38.28 
37.91 
36.28 
42.27 
39.50 
3636 
40.33 
42.27 
42.72 
SS.90 
34.75 
33.20 
38.01 
40.75 

Fixed 
Carbon. 

45.40 
46.26 
42.99 
46.82 
47.80 
46  .95 
46.45 
47.83 
4-3.09 
44.98 
40.71 
45.85 
45.38 
55.75 
54.58 
43.50 

Ash.       Sulj 

6.00         2. 
16.69        4. 
9.18 
10.13 
9.56 
3.49 
5.55        2 
12.84 
11.56 
7.37 
1304 
7.82 
10.93 
3.25 
1.64 
3.70 

)hur. 

41 
41 

63 

Pettis  

3.95 

St   Louis     . 

9  55 

Henry  

5  14 

La  Fayette  . 
Johnson. 

6.36 
7  29 

8  50 

2  97 

6  C2 

Livingston 

5  38 

Nodaway.  .  . 

3  53 

7  43 

8  94 

Cass  

7.80 

Cbarlton  .  .  . 

5  82 

Macon  .  . 

12.05 

Kansas. — The  Kansas  coal-measures  form  a  part  of  the  great 
Western  field  which  passes  through  the  eastern  half  of  the  State  from 
Iowa  and  Missouri  into  the  Indian  Territory,  with  an  outlying  area  of 
cretaceous  lignite  to  the  west  and  in  the  northern  central  part  of  the 
State.  The  main  portion  of  the  field  occupies,  approximately,  one- 
fourth  the  area  of  the  State. 

The  coal-measures  consist  of  three  kinds  of  rock  formations — 
sandstones,  limestones,  and  shales.  In  these  are  inclosed  the  beds  of 
coal,  which  do  not  occupy  anywhere  more  than  one-twentieth  of  the 
thickness  assigned  to  the  coal-measures,  and  over  large  parts  of  the 
area  there  is  no  coal  at  all.  A  few  square  miles,  with  one  bed  of  coal 
30  inches  thick,  would  be  a  rich  district,  and  there  are  several  such 
districts  in  eastern  Kansas.  The  bottom  of  the  lower  coal-measures  is 
tho  richest  horizon  of  the  formations.  It  is  in  this  horizon,  not  far 
from  the  Spring  River  boundary,  that  we  have  the  Weir  City  and 
•Scammon  coal-field,  of  Cherokee  County,  and  the  neighboring  coal- 
fields of  Frontenac  and  Pittsburg,  in  Crawford  County.  The  thickest 
and  best  seam  of  coal  in  Kansas  is  the  Cherokee  bed,  found  in  Chero- 
kee, Crawford  and  Labette  counties.  It  extends  from  the  Indian 


STEAM-BOILER  ECONOMY. 


Territory,  entering  the  State  near  Chetopa,  and  runs  across  the  south- 
east part  of  Labette  County,  the  west  and  northwest  parts  of  Cherokee,, 
and  southeast  part  of  Crawford,  and  enters  Missouri.  A  few  miles 
north  of  Columbus  the  coal-mining  region  begins,  and  we  have  a 
series  of  mining  towns — Scammon,  Weir  City,  Cherokee,  Fleming, 
Frontenac,  Pittsburg,  Arcadia,  Minden — around  which  the  coal  seam, 
whose  average  thickness  is  over  40  inches,  is  worked. 

Arkansas. — The  coal-measures  cover  an  area  of  9043  square  miles 
along  the  course  of  the  Arkansas  River  in  the  western  part  of  the 
State.  Two  beds  have  been  opened,  but  only  the  lower  is  of  workable 
thickness.  The  best  coal  yet  found  in  the  State  is  the  Spadra,  in 
Johnson  County,  3|  feet  thick  in  some  places.  The  following  analy- 
ses are  given  by  Macf arlane : 

Moisture. 

Sebastian  Co 1.40 

Long's 3.80 

Yell  Co 3.00 

Johnson  Co.  (11  in.)....  2.00 

Crawford  Co.  (1  ft.) 1.00 

Spadra  Creek 0.50 

The  analyses  show  these  coals  to  range  from  semi-anthracite  to- 
semi-bituminous. 

The  following  analyses  and  descriptions  of  Arkansas  coals,  made  in 
the  geological  survey  of  the  State  by  Dr.  R.  N.  Brackett  and  Mr.  J.  P. 
Smith,  were  published  in  "Mineral  Resources"  for  1888: 


Volatile  Matter.    Fixed  Carbon. 

Ash. 

1235               82.25 

4.00 

10.70               84.10 

1.40 

11.40               80.40 

5.20 

7.75               88.75 

1.50 

15.20               80.80 

3.00 

7.90               85.60 

6.00 

Names  of  Mines. 

Counties. 

Chemical  Composition. 

Water. 

Vol. 
Hydro- 
carbon. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Hackett  City  shaft.  .  . 
Huntington  slope  .... 
Greenwood  shaft  
Gwynn  drift        .        . 

Sebastian 
do 
do 
do 

do 
Johnson  . 
Franklin 
Pope 
Johnson 
do 
do 
Pope 

0.85 
0.93 
0.82 
0.89 

1.78 
0.87 
1.13 
0.98 
1.10 
1.02 
1.18 
1.06 

14.92 
15.55 

14.87 
14.58 

13.33 
14.13 
13.21 
12.20 

11.28 
10.84 
1048 
8.41 

73.87 
77.54 
75.82 
77.09 

76.23 
80.92 
81.28 
76.82 
7284 
76.12 
76.49 
75.43 

9.04 
4.85 
5.97 
6.25 

7.05 
3.09 
3.22 
8.17 
12.04 
8.35 
8.32 
11.75 

1.32 
1.14 
2.52 
1.19 

1.6* 
0.99 
1.16 
1.83 
2.75. 
3.67 
3.53 
3.35 

Western   Coal   and 
Mining  Company 

Philpott  shaft  

Ouita  slope      .          .  . 

Eureka  shaft  ...... 

Coal  Hill  shaft 

Allister  slope  

COAL-FIELDS  IN  THE   UNITED  STATES.  77 

The  above  coals  are  mostly  semi-bituminous.  To  the  eye  they  all 
present  more  or  less  the  appearance  of  soft  bituminous  coal  with  a 
cuboidal  fracture.  There  seems  to  be  no  approach  in  any  to  the  hard, 
compact,  glistening  anthracite,  with  the  semi-conchoidal  fracture. 
But  despite  these  facts  of  proximate  composition  there  are  several 
coals  of  this  list  which  from  their  mode  of  burning  deserve  to  be 
classed  as  semi-anthracites.  These  are  the  coals  from  the  Ouita,  the 
Eureka,  and  the  Shinn  openings.  The  remaining  coals  are  all  of  the 
nature  of  semi-bituminous  coals. 

Arkansas  coals  are  all  more  or  less  soft  and  friable,  and  not  well 
adapted  to  long  transportation.  This  characteristic  is  variable  in 
different  openings.  They  all  burn  freely  and  make  little  smoke  or  soot. 
For  reaching  the  best  results,  however,  a  grate  with  small  openings  is 
necessary,  as  these  coals  are  liable  to  decrepitate  and  to  fall  through  the 
grate.  Coal  Hill  coal  makes  an  intensely  hot  fire,  producing  steam 
rapidly  ;  but  it  clinkers  and  is  severe  in  its  action  upon  grate-bars. 
It  slacks  a  good  deal  on  exposure,  and  in  burning  much  fine  coal  is 
lost  through  ordinary  grate-bars.  Sebastian  County  coal  is  easily 
ignited  and  quick-burning,  but  does  not  produce  quite  so  intense  a 
heat  as  does  the  Coal  Hill  coal  ;  it  does  not  clinker,  but  leaves  a  loose 
ash.  The  Ouita  and  Eureka  coals  are  not  considered  good  for  steam- 
ing purposes. 

Indian  Territory. — The  coal-measures  cover  13,600  square  miles. 
At  McAlester  there  is  an  extensive  bed  of  bituminous  gas-. and  steam- 
coal,  which  is  also  worked  at  Savannah,  10  miles,  south,  and  at 
Atoka,  45  miles  south.  II.  M.  Chance  (Trans.  A.  I.  M.  E.,  1890) 
says : 

The  Choctaw  coal-field  is  a  direct  westward  extension  of  the 
Arkansas  coal-field,  but  its  coals  are  not  like  Arkansas  coals,  except 
in  the  country  immediately  adjoining  the  Arkansas  line. 

In  the  Mitchell  basin,  about  10  miles  west  from  the  Arkansas  line, 
coal  recently  opened  shows  19$  volatile  matter;  the  May  berry  coal, 
about  8  miles  farther  west,  contains  23$  volatile  matter;  and  the  Bryan 
Mine  coal,  about  the  same  distance  west,  shows  26$  volatile  matter. 
About  30  miles  farther  west,  the  coal  shows  from  38  to  41|  per  cent 
Tolatile  matter,  which '  is  also  about  the  percentage  in  coals  of  the 
McAlester  and  Lehigh  districts. 


78  STEAM-BOILER  ECONOMY. 


ANALYSES   OF   INDIAN  TERRITORY  COALS. 

Water.         JotaUte         Fixedn<  ^ 

Mitchell  Basin  ............  1.06  19.03  71.74  7.53  0.65 

Grady  Basin  ..............  1.79  40.21  51.79  4.88  1.33 

McKinney  District  ........  1.71  38.67  51.48  7.14  1.01 

Krebs,  McAlester  bed  ......  1.80  37.17  53.40  6.73  0.90 

Leliigk  mines  ............  4.32  40.51  48.47  8.10  2.60 

Atoka  ....................  6.66  35.42  57.52  6.60  3.73 

Choctaw  Nation.    ........  1.59  23.31  66.85  8.25  1.18 

Cherokee  .................  3.62  29.51  48.09  14.78  4.00 

.................  4.07  27.67  42.12  20.20  5.94 

"  Mineral  Resources  "  for  1889  says  of  the  coals  of  the  McAlester  bed 
mined  at  McAlester,  Krebs,  and  Alderson,  and  the  Grady  bed  mined 
at  Hartshorne,  "These  coals  compare  favorably  with  the  best  gas- 
coals  mined  in  the  country  (as  comparison  with  standard  Pittsburg 
coal  will  show),  and  they  are  by  far  the  best  coals  now  mined  in  the 
Southwest,  if  not  indeed  the  best  mined  west  of  the  Mississippi  River. 
They  are  in  every  way  vastly  superior  to  Kansas,  Missouri,  and  Iowa 
coals." 

Texas.  —  A  detached  portion  of  the  great  Missouri  coal-field  covers 
the  northeastern  portion  of  the  State  for  about  6000  sq.  miles.  The 
coal  is  a  regular  bituminous  of  the  Carboniferous  age.  Some  beds 
are  from  3  ft.  to  6  ft.  thick.  The  coal  is  usually  of  poor  quality,  high 
in  ash  and  sulphur.  Three  analyses  gave  the  following  : 

Localities.  Moisture.       Vol.  Mat.      Fixed  Carbon.       Ash.  Sulphur. 

Young  Co  ...............  10.00  30.75  46.59  11.96  0.70 

Fort  Worth  ..............  14.42  30.03  42.53  13.02  1.47 

"     ..............     4.60  34.72  49.27  11.41  1.56 

Cannel-coal  and  semi-anthracite  ave  also  been  found  in  Texas. 
In  the  Cretaceous  and  Laramie  coal-fields  of  the  Rio  Grande,  near  Eagle 
Pass,  bituminous  coal  of  good  quality  is  found.  It  is  superior  to  the 
Carboniferous  coals  of  the  State,  but  to  the  eastward  the  beds  are 
lignite  and  impure.  Lignites,  mostly  of  very  poor  quality,  contain- 
ing 10  to  20  per  cent  moisture  even  when  sun-dried,  are  found  in 
many  deposits  in  the  eastern  part  of  the  State.  The  San  Tom  as, 
Webb  Co.,  coal,  which  has  the  appearance  of  being  an  altered  lignite, 
is  a  very  serviceable  fuel,  and  is  largely  used  in  Laredo  and  on  the 
Mexican  National  Railroad. 

COALS   WEST   OF   THE    NINETY-SEVENTH    MERIDIAN. 

Colorado  Coals.  —  The  Colorado  coals  are  of  extremely  variable  com- 
position, ranging  all  the  way  from  lignite  to  anthracite.  G.  C.  Hewitt 
(Trans.  A.  I.  M.  E.,  xvii.  377)  says:  The  coal-seanis,  where  unchanged 


COAL-FIELDS  OF  THE   UNITED  STATES.  7& 

by  heat  and  flexure,  carry  a  lignite  containing  from  5  to  20  per  cent 
of  water.  In  the  sou tlieas tern  corner  of  the  field  the  same  have  been 
metamorphosed  so  that  in  four  miles  the  same  seams  are  an  anthracite, 
coking,  and  dry  coal.  In  the  basin  of  Coal  Creek  the  coals  are 
extremely  fat,  and  produce  a  hard,  bright,  sonorous  coke.  North  of 
Coal  Basin  half  a  mile  of  development  shows  a  gradual  change  from  a 
good  coking  coal  with  patches  of  dry  coal  to  a  dry  coal  that  will  barely 
agglutinate  in  a  beehive  oven.  In  another  half  mile  the  same  seam  is 
dry.  In  this  transition  area,  a  small  cross-fault  makes  the  coal  fat  for 
twenty  or  more  feet  on  either  side.  The  dry  seams  also  present  wide 
chemical  and  physical  changes  in  short  distances.  A  soft  and  loosely 
bedded  coal  has  in  a  hundred  feet  become  compact  and  hard  without 
the  intervention  of  a  fault.  A  couple  of  hundred  feet  has  reduced  the 
water  of  combination  from  12  to  5  per  cent. 

ANALYSES  OF  COLORADO  COALS. 

Moisture.  Vol.  Mat.    Fixed  Carbon.  Ash.  Sulphur. 

Sunshine,  Colo.,  average....  2.8  36.3  37.1  23.8              

Newcastle,    "            '.'       1.7  37.95  48.6  11.6              

ElMoro,        "             "       1.32  38.23  55.86  3.59            

Crested  Buttes,           "     1.10  23.20  72.60  3.10            

Lenox,  Huerfano  Co 2.92  41.18  45.36  10.54  1.39 

Rouse,         "          " 2.66  36.71  51.41  9.22  1.37 

Cbicosa,  Las  Animas  Co....  0.20  28.94  64.51  6.35  0.27 

Victor,       "          "        "....1.26  36.40  53.10  9.24  1.11 

Fairmount  vein,  La  Plata  Co.  1.25  39.71  52.90  6.14             t 

Porter  vein,          "       "       ".  0.63  34.70  57.30             7.37  0.74 

LIGNITES   AND   LIGNITIC    COALS   OF   THE   WESTERN   STATES. 

Lignite  is  the  next  stage  above  peat  in  the  formation  of  coal.  It 
varies  greatly  both  in  appearance  and  in  chemical  composition.  Its 
color  ranges  from  light  yellow  to  deep  brown  or  black.  The  lignites 
belong  to  a  later  geologic  period  than  the  Carboniferous.  They 
occur  principally  in  Cretaceous  and  Tertiary  formations.  The  beds, 
which  are  often  of  great  thickness,  present  the  same  general  charac- 
teristics as  those  of  the  true  coals.  Many  instances  occur  in  which 
portions  of  beds  of  lignite  have  changed  to  bituminous  and  even  to 
anthracite.  The  lignites  of  Western  America  resemble  the  "  brown 
coals  "  of  Europe  in  holding  a  large  amount  of  water,  the  percentage 
in  most  of  them  being  from  12  to  15,  though  some  have  as  low  as  4 
and  others  as  high  as  20  per  cent.  The  percentage  of  ash  is  usually 
low,  from  2  to  9  per  cent,  while  the  sulphur  is  generally  below  1  per 


80 


STEAM-BOILER  ECONOMY. 


cent.     The  following  analyses  are  given  by  Dr.  E.  W.  Raymond  in 
Trans.  A.  I.  M.  E.,  vol.  ii.,  1873: 


C. 

H. 

N. 

O. 

s. 

Moist- 
ure. 

Ash. 

Monte  Diablo   Cal    

59  72 

5  08 

1  01 

15  69 

3  92 

8  94 

5  64 

Weber  Canon    Utah  

64  84 

4  84 

1  29 

15.52 

1.60 

9.41 

3.00 

Echo  Canon,  Utah  

69.84 

390 

1.93 

10.99 

0.77 

9.17 

3.40 

64.99 

3.76 

1.74 

15.20 

1.07 

11.56 

1.68 

>  «            >  <           (i 

69  14 

4  86 

1  25 

9  54 

1.03 

8  06 

6.62 

Coos  Bay   Oregon  

56  24 

3.38 

0.42 

21  82 

0.81 

13.28 

4.05 

Alaska  

55.79 

3.26 

0.61 

19.01 

0.63 

16.52 

4.18 

67  67 

4  66 

1  58 

12  80 

092 

3  08 

9  28 

Canon  City,  Colo  
Baker  Co.,  Ore  

67.58 
60.72 

7.42 
4  30 

13.42 
14.42 

0.63 

2.08 

5.18 
14.68 

5.77 
3.80 

Wyoming. — In  the  Green  River  coal-basin  in  southwestern  Wyom- 
ing 250  ft.  of  coal  is  found  in  a  thickness  of  about  3000  ft.  of  coal- 
measures.  The  beds  are  numerous,  and  many  of  them  are  of  workable 
thickness.  Analyses  and  heating  values  of  various  coals  in  this  terri- 
tory are  given  in  Chapter  V,  on  the  Heating  Value  of  Coal. 

New  Mexico. — The  coals  of  New  Mexico  are  lignitic  coals  of  the 
Cretaceous  and  Tertiary  formations,  in  all  the  grades  from  anthracite 
to  true  lignite.  They  are  chiefly  used  by  the  railroads  crossing  the 
Territory. 

ANALYSES. 


Water. 

White  Oaks,  Lincoln  Ce. . .       2.35 

Vermejo  Pass 3  27 

Placer  anthracite. . .  2.90 


Volatile 
Matter. 

35.53 

23.73 

3.18 


Fixed 
Carbon. 

50.24 
59.72 
88.91- 


Ash. 

11.88 

13.28 

5.21 


Sulphur. 
0.61 


Arizona. — Several  beds  of  lignitic  coal  of  extremely  variable  com- 
position have  been  found  in  the  Territory.  Two  analyses  of  coals 
from  Deer  Creek,  Ariz.,  taken  from  locations  8  miles  apart  are  given 
below.  The  first  is  a  semi- bituminous  coal;  the  second,  a  lignite: 

i.  ii. 

Volatile  combustible  matter  and  water 14.5  47.6 

Fixed  carbon 61.0  44.0 

Ash ..... 24.5  8.4 

Utah.. — The  Green  River  coal-basin  contains,  according  to  Clarence 
King's  "  Geological  Exploration  of  the  40th  Parallel/'  "a  practically 
inexhaustible  supply  of  coal."  Beds  from  7  to  25  feet  thick  are  dis- 
covered at  intervals  over  500  miles,  and  from  their  ordinary  gentle  dip 
may  be  mined  with  unusual  ease.  Two  analyses  are  as  follows : 


COAL-FIELDS  OF  THE   UNITED  STATES.  81 

Moisture.      Vol.  Mat.      Fixed  Carbon.     Ash.  Sulphur. 

•Castledale 3.43  42.81  47.81*          9.73  

CedarCity 3.50  43.66  43.11*          5.95  

*  Includes  sulphur,  which  is  very  high.    Coke  from  Cedar  City  analyzed  :  Water  and  volatile 
matter,  1.42;  fixed  carbon,  76.70;  ash,  16.61;  sulphur,  5.27. 

Montana. — The  coals  of  Montana  are  all  of  Cretaceous  age.  They 
embrace  a  wide  variety  of  true  bituminous  coals,  found  only  in  or  near 
the  mountains,  and  the  inferior  lignites  whose  seams  form  prominent 
parts  of  the  series  of  rocks  that  underlie  the  Great  Plains  country. 
These  lignites  have  been  mined  at  a  few  localities,  but  their  low  heating 
power  and  rapid  crumbling  unfit  them  for  general  use,  and  the  bitumi- 
nous coals  have  occupied  the  market.  The  lignites  differ  from  the 
true  coals  in  two  important  particulars :  they  contain  a  large  amount  of 
moisture  and  they  crumble  upon  exposure  soon  after  mining.  The 
moisture  makes  them  of  low  heating  power,  and  their  rapid  crumbling 
unfits  them  for  transportation  and  is  a  serious  detriment  in  burning.  An 
average  analysis  of  the  lignites  of  eastern  Montana  shows:  Water, 
12-15;  volatile  carbon,  40-45;  fixed  carbon,  30-35;  ash,  5-10. 

The  bituminous  coals  of  Montana  occur  in  small  isolated  fields 
within  the  mountain  region  and  in  a  great  belt  of  coal  land  that 
extends  along  the  eastern  front  of  the  Rocky  Mountains. 

The  character  of  the  coals  varies  widely  in  different  seams  and  at 
different  fields.  Long-  and  short-  flamed,  coking  and  noncoking  coals 
occur  sometimes  in  adjoining  seams  of  the  same  mine.  As  a  whole 
the  coals  contain  a  high  percentage  of  ash,  and  would  not  rank  high  in 
more  favored  localities.  Some  of  the  coals,  however,  are  as  pure  as  the 
.best  of  Wyoming  or  Colorado  fuels. 

North  Dakota. — The  coal  of  North  Dakota  is  a  lignite  of  inferior 
quality  and  does  not  compare  favorably  with  that  brought  from  other 
.localities.  ("Mineral  Resources/'  1891.) 

Nevada. — A  bed  of  coal,  5  to  6  feet  thick,  20  miles  east  of  Eureka, 
is  mined  for  local  consumption. 

California. — The  Mt.  Diablo  coal-field  contains  several  beds,  which 
vary  greatly  in  thickness.  The  coal  is  of  rather  inferior  quality.  Coal 
has  been  found  in  many  portions  of  the  State,  but  the  beds  are  mostly 
small  in  extent  and  the  quality  poor.  Nearly  all  of  the  coal  of  Cali- 
fornia is  lignite,  that  from  Monterey  County  alone  being  classed  as 
bituminous.  San  Francisco  is  dependent  for  its  coal  supply  chiefly  on 
coals  brought  by  water  from  other  States  and  from  foreign  countries. 
An  analysis  of  Mt.  Diablo  coal  is  as  follows: 


82  STEAM-BOILER  ECONOMY. 

Moisture 14.69 

Volatile  matter 83.89 

Fixed  carbon 46.84 

Ash 4.58 

Oregon. — The  developments  are  confined  to  the  coal-basin  in 
Coos  County,  though  other  lignite  discoveries  have  been  reported. 
The  field  covers  several  hundred  square  miles  of  territory,  stretching 
from  the  coast  15  or  20  miles  inland.  The  coals  are  true  lignites,  very 
high  in  water  and  volatile  matter.  Coal  is  loaded  direct  from  the 
mines  at  Marshfield  to  Pacific  Ocean  steamers  and  sold  principally  in 
San  Francisco. 

Moisture.  Vol.  Mat.  Fixed  Carbon.  Ash.  Sulphur.. 

Coos  Bay 15.45            41.55            34.95  8.05  2.53 

••       ..  17.27           44.15            32.40  6.18  1.37 

YaquinaBay 13.03            46.20            32.60  7.10  1.07 

John  Day  River 4.55            40.00            48.19  7.26  .60 

"     6.54           34.45            52.41  5.95  .65 

Washington. — The  developed  coal-fields  lie  chiefly  in  a  compara- 
tively narrow  belt,  running  nearly  due  north  and  south,  thrtfugh  the 
western  portions  of  Whatcom,  Skagit,  Snohomish  and  King  counties 
into  Pierce  and  Thurston  counties.  Some  distance  to  the  east  of  the 
southern  end  of  this  belt,  in  Kittitas  County,  extensive  operations  have 
been  carried  on  for  a  number  of  years.  The  main  belt  extends  along 
the  Cascade  Range,  and  important  mines  have  been  opened  on  both 
the  eastern  and  western  slopes  of  the  range.  Coal  is  found  also  in 
other  localities,  notably  in  Lincoln,  Spokane,  Cascade,  and  Okanogan 
counties.  The  coals  of  the  State  embrace  lignite,  semi-bituminous, 
and  bituminous.  The  total  area  of  the  coal  deposits  of  Washington 
has  not  been  determined,  but  there  is  no  doubt  that  almost  inexhaust- 
ible supplies  are  at  hand,  not  only  for  the  future  demand  of  its  popu- 
lation, but  sufficient  to  furnish  a  basis  for  profitable  traffic  for  trans- ' 
portation  to  the  entire  Pacific  Coast.  ("Mineral  Resources,"  1894.) 

The  Bellingham  Bay  coal-bed  is  14  ft.  thick,  one-half  of  which  is 
mined,  the  lower  half  being  of  no  value.  At  Renton  two  beds  are 
worked,  the  upper  17  ft.  thick,  yielding  10  ft.  of  good  coal,  and  the 
lower  11  ft.  thick,  with  8  ft.  of  good  coal.  The  Seattle  mine,  10 
miles  southeast  of  Seattle,  has  two  workable  beds,  5  ft.  and  8  ft.,  of 
good  coa/. 

ANALYSES. 

Localities.  Moisture.        Vol.  Mat.  Fixed  Carbon.  Ash.  Sulphur. 

Bellingham  Bay 8.39  3326  45.59  12.66 

Seattle..  .   11.66  45.98  35.49  6.44  0.43 


COAL-FIELDS  OF  THE   UNITED  STATES.  83 

Alaska, — The  coal-fields  of  Cook  Inlet  are  described  in  the  17th 
and  20th  Annual  Reports  of  the  U.  S.  Geological  Survey.  The  coal 
is  a  low-grade  lignite.  In  appearance  it  is  often  hardly  more  than  a 
compressed  mass  of  carbonized  wood.  The  composition  is  quite  vari- 
able, as  shown  by  the  following  analyses : 

Locality.  Moisture.  Volatile  Carbon.  Ash'  Sulphur. 

Wood-coal,  4  miles  W.  of  Tyonek.      5.41        65.13  27.60  1.86        0.26 

6  miles  W.  of  Tyonek 9.44  48.75  33.56  8.25        0.49 

Bradley  seam,  Kacliemak  Bay...     12.64  43.96  37.14  6.86        0.49 

Curtis  seam,            "            "   11.67  52.37  21.01  14.95        0.46 

Two  fields  on  the  southeastern  coast,  the  upper  on  the  shores  of 
Controller  Bay,  and  the  lower  reaching  40  miles  westward  from  Icy 
Bay,  have  been  investigated  and  coal  has  been  found  in  seams  from  10 
to  27  ft.  thick.  The  coal  has  a  bright,  black  lustre  and  conchoidal 
fracture,  and  has  all  the  characteristics  of  semi-anthracite  except  hard- 
ness and  specific  gravity.  Two  analyses  are  given  from  samples  taken 
from  outcrops  at  opposite  ends  of  the  upper  coal-field,  showing  great 
uniformity. 

T^aHtTT  Adhering    Volatile        Fixed         Aor,        c  ,  , 

Locality.  Water.      Matter.       Carbon.       Ash-       Sulphur. 

„.,,,,  l       0.75        13.25        82.40       3.60       0.69 

ControllerBay ]       a78       ^       ^       5.70       2.90 


CHAPTER  V. 

TESTS  OF    THE    HEATING  VALUE    OS   AMERICAN   AND   FOREIGN- 
COALS. 

Johnson's  Tests  of  American  Coals. — The  series  of  tests  of  Amer- 
ican coals  made  by  Prof.  Walter  E.  Johnson  for  the  United  States 
Navy  Department  in  1842  and  1843,  the  report  of  which  was  pub- 
lished in  a  government  document  covering  600  pages,  is  often  referred 
to  by  writers  on  the  subject  of  coal.  The  author  made  a  careful 
study  of  Prof.  Johnson's  report,  and  published  his  conclusions  concern- 
ing it,  and  also  concerning  the  tests  of  Scheurer-Kestner  and  Meu- 
nier-Dollfus  in  1868,  in  a  series  of  articles  entitled  "  Critical  Review 
of  Efficiency  Tests  of  Coals  "  in  The  Engineering  and  Mining  Journal 
in  October,  1891.  It  was  shown  in  this  review  that  Johnson's  results 
are  of  little  use  in  determining  the  relative  value  of  American  coals 
when  burned  under  the  conditions  of  modern  practice.  The  boiler 
used  by  Johnson  was  of  the  two-flue  type,  set  only  9  to  10  inches  from 
the  grate-bars,  the  furnace  being  entirely  unsuited  for  bituminous 
coal.  Some  of  the  anthracites  were  burned  with  an  excessive  air-sup- 
ply, causing  them  to  give  results  much  below  those  that  may  be  ob- 
tained under  favorable  conditions.  The  table  on  the  next  page  is  a 
condensed  summary  of  the  evaporative  results  obtained  from  the  several 
coals,  as  determined  by  the  boiler-tests. 

Scheurer-Kestner's  Tests  of  European  Coals. — A  series  of  tests  of 
European  coals  was  made  by  Scheurer-Kestner  and  Meunier-Dollfus 
in  1868,  and  the  results  were  reported  in  the  Bulletin  de  la  Societe 
Industrielle  de  Mulhouse.  An  excellent  study  of  these  tests,  with 
others,  is  that  by  M.  L.  Gruner  in  his  papers  on  "  The  Classification 
and  Heating  Power  of  Coals,"  translated  from  the  French  by  R.  P. 
Rothwell,  and  published  in  the  Engineering  and  Mining  Journal,  July 
18th,  1874,  et  seq. 

Gruner  divides  the  bituminous  coals  into  five  classes  as  follows: 

1.  Dry  or  semi-bituminous  anthracitic  coals. 

84 


TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


85 


RESULTS  OF  JOHNSON'S  TESTS  CORRECTED  AND  COMPARED  BY 
PER  CENT  OF  FIXED  CARBON  TO  TOTAL  COMBUSTIBLE. 


Number  of  C°al,  ar-  ' 
ranged  geographic- 
ally. 

^S 

1 

055 

fell 
IE  O..Q 

O 

Name  of  Coal. 

Evaporation  f  rom  and 
at  212°  per  Ib.  Com- 
bustible. Johnson's 
figures  corrected  by 
multiplying  by  1.066. 

fei® 
al 

^"5  3  u 
V, 

!§§| 

.*  o,c^ 
JL, 

Ml 

nl 

y°* 

11J1 
> 

Equivalent  of  Evap- 
oration in  Calories.* 

1 
2 
3 
4 
5 
6 
7 

8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 

20 
21 
22 
23 

24 
25 

26 

27 

28 
29 
30 
31 
32 
33 

15 
14 
9 
8 
23 
11 
10 

3 
13 
7 
1 
5 

6 

12 

2 

20 
16 
17 

21 
18 
19 
28 
24 
27 
26 
31 

22 
'29 
30 
25 
32 
33 

Anthracites,  Penn. 
Beaver  Meadow  slope  No.  3  

11.15 
11.29 
11.52 
11.59 
10  26 

97.4 
97.2 
95.6 
96.8 
94.4 
95.7 
92.4 

85.6 

85.5 
83.6 
83.2 
82.7 
84.3 
83.2 
83.8 
80.1 
79.1 
77.2 
77.5 

71.1 
60.9 
64.3 
61.3 
65.0 
63.8 
59.9 
63.2 

67.2 
73.9 

57.8 
61.4 
54.9 

2.6 

2.8 
4.4 
3.2 
5.6 
4.3 
7.6 

14.4 
14.5 
16.4 
16.8 
17.3 
15.7 
16.8 
16.2 
19.9 
20.9 
22.8 
22.5 

28.9 
39.1 
35.7 
38.7 
35.0 
36.2 
40.1 
36.8 

32.8 
26.1 
42.2 
38.6 
45.1 

5988 
6063 
6186 
6224 
5509 
6159 
6176 

6417 
6068 
6261 
6653 
6315 
6396 
6?72 
6138 
6455 
56CO 
5859 
5805 

5574 
5708 
5(565 
4914 
5273 
4914 
5123 
4425 

5558 
4865 
4726 
5252 
4419 
2696 

"      No.  5  . 

Lehigh  

Lackavvanna     

11.47 
11.50 

11.95 
11.30 
11.66 
12.39 
11.76 
11.91 
11.68 
11.43 
12.03 
10.54 
10.91 
10.81 

10.38 
10.63 
10.55 
9.15 
9.82 
9  15 
9.54 
8.24 

10.35 
9.06 
8.80 
9.78 
8.23 
5.02 

Semi-  Bituminous. 
N.  Y.  &  Md.  Mining  Co.  ,  Md  
Neff'  s  Cumberland,  Md  

p]asby's  Md  

Atkinson  &  Templeman,  Md  

Easby  &  Smith's   Md      ... 

Dauphin  &  Susquehanna   Pa  ,    . 

Blossburg,  Pa  

Lycorning  Creek,  Pa  

Quin's  Run,  Pa  ...         .... 

Karthaus    Pa  

Cambria  Co.,  Pa  

Barr's  Deep  Run,  Va.   „  

Bituminous,  U.  8. 
Crouch  &  iSnead,  Va  

Chesterfield  Mining  Co.,  Va  

Creek  Co.  ,  Va  

Clover  Hill,  Va  

Pittsburo-   Pa  .... 

Bituminous,  Foreign. 
Pictou   N.  S  

Sidney.  N.  S  

Liverpool,  Eng  

Newcastle,  Eng  

Scotch,  Scot.   

Dry  Pine  Wood  

*  A  calorie  is  the  amouut  of  heat  required  to  raise  1  kilogram  of  water  1°  centigrade  = 
3.968  B.  T.  U.  When  used  as  a  measure  of  the  heating  value  of  a  fuel  it  is  the  number  of  units 
of  weight  of  water  which  may  be  heated  1°  C.  by  the  combustion  of  1  unit  of  weight  of  the 
fuel.  The  unit  of  wHtrht  IHHV  l.~  eiih'-r  u  g-am,  a  kilogram  or  a  pound.  When  thus  used  a 
ca  orie  is  equivalent  to  l.b  British  thermal  units. 


86  STEAM-BOILER  ECONOMY. 

2.  Short-flaming,  caking,  or  coking-coals. 

3.  True  coking-coals,  or  smiths'  coals. 

4.  Long-flaming,  caking,  or  gas-coals. 

5.  Long-flaming,  dry  coals. 

The  range  of  chemical  analysis,  theoretical  heating  power,  and 
value  for  steam  making  of  European  coals  as  determined  by  boiler 
tests  is  shown  in  the  table  on  the  following  page,  in  which  are  arranged 
a  number  of  results  of  tests  and  analyses  taken  by  Gruner  from  Scheurer- 
Kestner's  reports.  The  total  heating  power  (in  calories)  is  that  found 
by  tests  with  Favre  and  Silbermann's  calorimeter,  and  it  is  notably 
higher  than  the  theoretical  power  obtained  by  Dulong's  formula,  except 
in  the  case  of  the  highly  bituminous  lignite  from  Bohemia,  which  is 
said  to  resemble  a  petroleum. 

The  next  to  the  last  column  in  the  table  gives  the  range  of  thd  in- 
dustrial heating  power,  or  steaming  power,  in  calories,  of  the  sevyral 
classes  of  Gruner,  as  determined  by  boiler  tests,  and  the  last  column 
the  per  cent  of  this  so-called  industrial  heating  power  to  the  total 
heating  power  as  determined  by  calorimeters.  From  this  oolirnn  it 
appears  that  the  short-flaming,  caking,  or  coking  coals  containing  on 
an  average  about  78  parts  of  fixed  carbon  in  100  of  total  combustible, 
have  a  higher  ratio  of  industrial  to  total  heating  power  than  the 
anthracite  coals,  and  a  much  higher  ratio  (as  65  to  55)  than  the  long- 
flaming,  dry  coals,  averaging  55  parts  of  fixed  carbon  in  100  of  total 
combustible. 

The  results  in  this  table  are  figured  upon  pure  and  dry  coal,  that 
is,  the  ash  and  moisture  have  been  deducted  and  the  calculation  made 
on  the  basis  of  the  ratio  which  the  fixed  carbon  bears  to  the  total  of 
fixed  carbon  and  volatile  combustible  alone.  This  is  a  more  scientific 
method  than  that  which  includes  the  moisture  and  ash,  which  may  be 
called  accidental  impurities,  and  leads  to  less  confusion  and  to  more 
correct  conclusions  concerning  the  influence  of  the  volatile  combusti- 
ble upon  the  heating  power. 

The  principal  results  shown  in  the  tables  of  Johnson's  and  Scheu- 
rer-Kestner's  tests  are  plotted  in  the  diagram  on  page  88,  showing 
a  comparison  of  the  calorimetric  and  theoretical  heating  power  and 
the  industrial  or  steaming  power  of  the  coals  tested  by  Scheurer-Kest- 
ner,  and  of  the  average  of  Gruner's  five  classes,  with  the  results  of 
Johnson's  tests.  The  upper  line  of  the  diagram  shows  the  total  heating 
power  of  the  coals  tested  by  Scheurer-Kestner,  arranged  from  left  to 
right  in  the  order  of  their  percentages  of  fixed  carbon  to  tot;;l  com- 


TESTS   OF  THE  HEATING    VALUE  OF  COALS. 


87 


HEATING  POWER  OF  COALS,  ACCORDING  TO  SCHEURER-KESTNER 
AND  OTHERS,  AS  COLLATED  BY  GRUNER.  ARRANGED  IN 
ORDER  OF  PER  CENT  OF  FIXED  CARBON  IN  PURE  DRY  FUEL. 


Description  of  the  Fuel. 

Proportion  of  Fixed 
Carbon  in  Coke  per 
100  of  Fuel  dry  and 
free  from  Ash. 

Elementary 
Composition. 

Total  actual  Heating 
power,  calories. 

Heating  power  ac- 
cording to  Dulong's 
law,  calories. 

Industrial  Heating 
power  in  Steam 
Boilers. 

i  Industrial  Heating 
power  per  cent  of 
total,  average. 

C. 

H. 

0  +  N* 

Anthracite  coal  from  the  Creusot  ........ 

G  rimer's  Class  5.  Dry  or  semi-bituminou8 
anthracitic  coals  

88.1 
(82 

v° 

90 

84.2 

80.4 
^74 
•\  to 
(83 

73.0 

(68 

8 

70.3 
64.4 
(60 
-(  to 
68 
63.5 
60.6 
60.4 
59.0 

58.5 
(50 
•ho 
(60 
55.0 
52.0 
51.4 
50.4 
48  8 
46.8 
(38 
•jto 
30 

92.36 
90 
to 
93 
9U.79 

88.48 
88 
to 
91 

84.47 
88.32 
84 
to 
89 
83.94 
83.55 
SO 
to 
85 
83.82 
78.58 
81.56 
76.87 

78.97 
72 
to 
80 
76.58 
72.98 
67.60 
66.51 
70.57 
66.31 

44.44 

3.66 
4.5 
to 
4. 
4.24 

4.41 
5.5 
to 
4.5 

4.21 
4.79 
5. 
to 
4.5 
4.43 
5.17 
5.8 
to 
5. 
4.60 
5.23 
4.98 
4.68 

4  67 
5.5 
to 

4.5 
8.27 
4.04 
4.55 
4.72 
5.44 
4.85 

6.17 

3.98 
5.5 
to 
3. 
4.97 

7.11 
6.5 
to 
5.5 
11.32 
6.89 
11. 
to 
5.5 
11.63 
11.48 
14.2 
to 
10. 
11.58 
16.19 
13.46 
18.45 

16.36 
19.5 
to 
15. 
15.15 
22.98 
27.85 
28.77 
23.99 

as.  84 

49.39 

9456 
9200 
to 
9500 
9263 

9622 

9300 
to 
9600 
9257 
9077 
8800 
to 
9300 
9050 
8603 
8500 
to 
8800 
8724 
8325 
8462 
8215 

8457 
8000 
to 
8500 
7924 
6480 
6311 
6358 
73(53 
7006 

3622 

8552 

8683 
8363 

7789 
8494 

"7810 
8024 

'  7858 
7455 
7727 
7032 

7287 

838*7 
6300 
£831 
5760 
6542 
5788 

3590 

5760) 
to    J- 
6080  ) 

63.9 

65.0 
62.3 

58.8 

55.1 

Dry-burning  coal,  St.  Paul  du  Creusot.... 
Short-flaming   or   fat  coal,  C.iaptal  du 

Gruner's  Class  4.    Short-flaming,  caking 

5888) 
to    [ 
6400  \ 

'5376  ) 
to    J. 

5888  ) 

Caking  coal.    Ronchamp  

Or  uner's  Class  3.    True  caking  coals,  or 
smiths'  coals        

"4864) 
to    V 
5312  j 

'4288')' 
to   Y 
4800  1 

G  rimer's  Class  2.    Long  flaming,  caking 
or  gas-coals  ....                .... 

Long-flaming,  caking  coal.    Duttweiler  .  . 
Lontr-ttcuning  dry  coal      Montceau.. 

Very  long-flaming  coal.     Von  der  Heyclt 
Long-flaming,  dry  coal,     Louisenthal    ... 
Long-flaming,  semi-coking  coal.     Fried- 
richstall  

Gruner's   Class    1.      Long-flaming,    dry 

Highly  bituminous  lignite,  Bohemia  

Bituminous  wood   
Fossil  wood   passing  into  lignite 

Cellulose  C12Hi0O10 

*The  nitrogen  rarely  exceeds  1  per  cent. 

bustible.  The  five  numbered  stars  in  the  line  show  the  position  of 
the  averages  of  Gruner's  classes.  The  next  lower  heavy  line  in  the 
diagram  shows  the  theoretical  heating  value,  according  to  Dulong's  law, 
of  the  coals  tested  by  Scheurer-Kestner.  This  value  is  less  than  the 
total  value  in  every  case  except  that  of  the  bituminous  lignite.  The 
apparent  irregularities  in  this  line  as  compared  with  the  line  represent- 
ing the  total  heating  value  will  be  referred  to  hereafter.  For  com- 
parison with  these  two  lines  there  has  also  been  inserted  the  curve 


88 


STEAM-BOILER  ECONOMY. 


plotted  from  the  more  recent  results  of  Mahler,  which  are  hereafter 
discussed. 

Johnson's  tests,  as  shown  in  the  diagram,  group  themselves  into 
three  distinct  classes.     They  are  numbered  from  1  to  32,  in  the  order 


10,000 


4,000 


100 


90  80  70  60  50 

Fixed  Carbon,  Percent  of  Total  of  Carbon  and  Volatile  Combustible  Matter. 


FIG.  5. — COMPARISON  OF  CALORIMKTRIC  AND  THEORETICAL  HEATING  POWER 
AND  INDUSTRIAL  OR  STEAMING  POWER  OP  FOREIGN  AND  AMERICAN 
COALS.  (GRUNER,  SCHEURER-KESTNER,  AND  JOHNSON.) 

of  their  steaming  value.  The  extreme  irregularity  of  these  tests  is 
clearly  shown  by  the  position  of  the  numbers.  The  five  short  inclined 
lines  included  among  Johnson's  groups  represent  the  range  of  the  in- 
dustrial value  of  Gruner's  five  classes.  They  show  as  close  an  agree- 
ment as  can  be  expected  with  the  results  of  Johnson,  and  indicate 
that  the  efficiency  of  the  coals  in  actual  trial  upon  which  Gruner's 
figures  are  based  was  about  as  low,  on  an  average,  as  the  efficiency 


TESTS  OP  THE  HEATING    VALUE  OF  COALS.  8& 

shown  in  Johnson's  tests.  This  efficiency,  as  shown  in  the  last  col- 
umn of  the  table  on  page  85,  ranged  from  65  down  to  55  per  cent  of 
the  total  heating  value. 

In  the  author's  paper  in  The  Engineering  and  Mining  Journal, 
October  31,  1891,  the  following  remarks  were  made  on  Scheurer-Kest- 
ner's  tests : 

"  In  order  to  find  a  reason  why  the  theoretical  heating  power  of  the 
coals  tested  by  Scheurer-Kestner  is  less  than  the  actual  heating  power 
as  determined  by  a  calorimeter,  we  have  recourse  to  the  translation  of 
Gruner's  paper  before  referred  to,  from  which  the  following  extracts 
are  taken : 
"  Dulong  proposed  the  formula 

P  =  8080(7  +  34,462  (#  -  - 


where  P  =  heating  power,  0  =  weight  of  carbon,  0  —  weight  of  oxy- 
gen, H  =  free  hydrogen,  i.e.,  total  hydrogen  less  that  already  burnt 
to  water  by  the  oxygen  which  the  coal  contains. 

"  In  this  formula  the  influence  of  molecular  constitution  in  the  ca- 
loricity  of  bodies  was  ignored,  as  it  was  not  known  that  the  heat  of 
combustion  of  a  body,  simple  or  compound,  is  in  general  greater  in 
proportion  as  the  molecular  constitution  is  less  advanced. 

' '  It  is  now  established  by  the  labors  of  Favre,  Silbermann,  Kegnault, 
Berth elot,  and  others,  that  the  heat  of  combustion,  like  specific  heat, 
varies  with  the  density. 

Calories. 

Carbon  from  charcoal  develops 8080 

Carbon  of  gas-retorts,  which  is  more  dense 8047 

Natural  graphite 7797 

The  diamond  only 7770 

"  It  follows  from  this  that  to  apply  Dulong's  formula  to  coals  we 
should  substitute  for  the  calorific  power  of  hydrogen  in  a  gaseous  state 
that  of  hydrogen  in  a  solid  state,  and  instead  of  8080,  which  represents 
the  heat  of  combustion  of  carbon  having  a  density  greater  than  2,  we 
should  put  a  greater  number,  corresponding  to  the  less  condensed  state 
of  the  carbon  in  coals. 

"  Favre  and  Silbermann  determined  as  long  ago  as  1852  the  heat  of 
combustion  of 'the  following  isometric  hydrocarbons,  represented  by 
the  formula  C2,vH2n : 

Calories.  Calories. 


Olefmnt  gas,  C4H4. . .  11,858 

Amylene,  C,0HIO 11,491 

Panunyleue,  CaoHao..  11,303 


Carbure,  C22H23 11,262 

Cetene,  C32HS2      ....  11,118 
Metanylene,  C40H40..   10928 


"  From  these  last  five  numbers  corresponding  to  liquid  hydrocarbon,. 
MM.  Favre  and  Silbermann  concluded  that  with  each  addition  of  C.LL 


$0  STEAM-BOILER   ECONOMT. 

the  heat  of  combustion  diminishes  37.48  calories  per  unit  of  weight  of 
the  compound.  The  same  diminution  of  calorific  power  is  found  in 
the  ternary  compounds.  All  heat  set  free  in  the  act  of  condensation 
is  lost  beyond  recovery  by  the  act  of  combustion.  Now,  coals  are 
ternary  compounds  condensed  to  various  degrees,  and  this  is  why 
a  simple  elementary  analysis,  which  determines  nothing  as  to  the 
mode  of  combination,  can  teach  us  nothing  as  to  their  calorific  power, 
and  therefore  does  not  indicate  their  industrial  value, 

"Prof.  Stein,  of  Dresden,  goes  still  further  and  asserts  that  '  an 
elementary  analysis  teaches  us  nothing  about  the  actual  properties  of 
coal.'  This  assertion  appears  too  general;  it  is  also  in  opposition  to 
the  conscientious  work  of  Regnault,  who  concluded  from  his  analyses 
*  that  the  elementary  composition  of  coals  of  the  carboniferous  forma- 
tion and  of  the  same  quality  varies  only  within  very  narrow  limits/ 

"  M.  Gruner  explains  the  difference  between  the  conclusions  of  these 
two  chemists  by  the  very  great  difference  in  the  character  of  the  coals 
tested  by  each;  we  cannot,  therefore,  he  says,  'generalize  the  conclu- 
sions of  Prof.  Stein,  and  they  should  not  be  considered  as  applying  to 
the  coals  of  other  fields,  nor  on  the  other  hand  could  we  admit  without 
restrictions  the  opposite  conclusions  of  M.  Regnault.' 

"  The  elementary  composition  of  coals  does  not  always  agree  with 
their  essential  properties,  i.e.,  with  their  caking  and  heating  powers. 
This  disagreement  shows  itself  in  a  very  striking  manner  in  the  direct 
determination  of  the  heating  power  of  certain  coals,  as  made  by  MM. 
Scheurer-Kestner  and  Ch.  Meunier.  These  investigations  agree  also 
with  the  general  results  obtained  in  industrial  tests  made  by  Dr.  Brix 
in  Berlin,  and  by  the  French  and  English  navies.  From  a  study  of 
these  results  M.  Gruner  concludes  that  '  the  real  value  of  a  coal  may 
be  better  determined  by  a  proximate  than  by  an  elementary  analysis.' 

"  The  proximate  analysis,  which  consists  in  distilling  coal  in  a  retort 
and  burning  the  residue,  enables  us  to  determine  directly  the  caking 
power  as  well  as  the  nature  and  amount  of  ash.  It  is  also  easy  to  show, 
especially  by  Scheurer-Kestner  and  Meunier's  work,  that  the  heating 
power  increases  and  decreases  with  the  proportion  of  fixed  carbon  left 
by  the  distillation.  This  is  true  at  least  for  bituminous  coals,  but  not 
always  for  anthracites  and  lignites. 

"  Comparing  the  different  numbers  in  Scheurer-Kestner's  tests,  says 
Gruner,  we  perceive  that  several  coals  almost  identical  in  composition 
have  very  different  heating  power;  the  heat  of  combustion  increases 
and  decreases  with  the  proportions  of  coke,  and  seems  to  depend  espe- 
cially on  the  volatile  elements/' 

Commenting  on  these  observations  of  Gruner,  the  author  said  in 
Eng.  and  Mining  Journal,  Oct.  31,  1891 : 

"  Gruner  shows  that  the  less  the  density  of  any  form  of  carbon,  the 
greater  is  its  heating  power.  The  tests  he  records  also  show  that  coals 
containing  hydrogen  give  a  greater  heating  power  than  that  calculated 
~by  theory  from  their  elementary  composition.  It  would  naturally  be 


TESTS  OF  THE  HEATING    VALUE  OF  COALS,  91 

inferred,  therefore,  that  the  coals  which  have  the  least  density,  and 
which  contain  the  largest  percentage  of  disposable  hydrogen,  would 
have  the  greatest  heating  power.  Yet,  the  reverse  of  this  appears  to 
be  true,  so  that  after  the  disposable  hydrogen  reaches  4$  its  further 
increase  seems  to  be  actually  accompanied  by  a  decrease  of  heating 
power,  as  determined  by  a  calorimeter,  and  by  a  still  greater  relative 
decrease,  as  shown  in  the  diminution  of  efficiency,  from  65$  to  55$, 
in  the  industrial  or  steaming  power. 

"It  is  difficult  to  explain  the  anomaly,  except  upon  the  hypothesis 
that  the  calorimetric  determinations  of  the  more  volatile  coals  were  in- 
accurate. This  is  quite  possible,  for  Scheurer-Kestner  and  Meunier 
claim  to  have  improved  Favre  and  Silbermann's  calorimeter  so  as  to 
render  the  combustion  of  carbon  more  perfect.  May  it  not  be  possible 
that  they  did  not  so  far  improve  it  as  to  insure  the  combustion  of  all 
the  hydrogen  in  the  coals?  We  know  that  there  is  great  difficulty  in 
making  a  complete  combustion  of  the  volatile  matter  of  a  highly 
bituminous  coal  in  a  boiler  test,  as  was  shown  in  Johnson's  tests,  in 
which  dense  volumes  of  smoke  escaped  from  the  chimney  and  the  flues 
were  coated  with  soot,  and  as  also  is  shown  in  every-day  practice  with 
soft  coal.  Is  it  not  highly  probable  that  the  same  difficulty  exists  in 
some  degree  in  making  complete  combustion  of  these  coals  in  a  calori- 
meter? This  difficulty  is  further  indicated  by  the  considerable  differ- 
ence which  exists  in  the  result  of  the  calorimetric  determinations  of 
the  elements  as  published  by  different  physicists,  such  as  Andrews, 
Favre  and  Silberniaim,  and  Depretz. 

"There  is  certainly  room  for  redetermination  of  these  results  by 
modern  experimenters  with  improved  apparatus. 

"  If  such  tests  should  be  made  in  the  future,  I  would  suggest  the 
following  crucial  test  of  a  calorimeter,  namely,  determine  carefully  the 
total  heating  values  of  a  very  pure  anthracite,  low  in  hydrogen,  and  of 
refined  petroleum.  Then  mix  the  very  finely  powdered  anthracite  into 
a  paste  with  the  petroleum  in  different  proportions,  and  determine  the 
heating  value  of  the  mixtures.  It  should  be  the  same  as  that  calcu- 
lated from  the  percentage  of  the  two,  and  the  difference,  if  any,  would 
indicate  the  imperfection  of  the  calorimeter  for  determining  the  heat- 
ing power  of  a  fuel,  one  portion  of  which  is  more  volatile  than  the 
other.  It  is  possible  that  considerable  difficulty  would  be  met  with  in 
providing  such  conditions  in  a  calorimeter  that  both  portions  of  the 
mixture  could  be  completely  burned  at  the  same  time,  and  this  diffi- 
culty would  always  be  met  in  attempting  to  burn  any  highly  bitumi- 
nous coal." 

Since  the  above  was  published  Mahler's  tests  in  France,  and  Lord 
and  Haas's  in  the  United  States,  have  shown  that  there  is  an  exceed- 
ingly close  agreement  between  the  heating  value  determined  by  a 
bomb  calorimeter  of  the  Berthelot  type  and  that  computed  from  the 
ultimate  analysis  by  means  of  the  Dulong  formula.  Scheurer-Kestner'g 
results  are  therefore  now  discredited,  and  his  attempted  explanation 


92  STEAM-BOILER  ECONOMY. 

of  why  the  theoretical  heating  power  is  less  than  the  actual  is  of  no 
yalue. 

Mahler's  Tests  of  European  Coals. — MM.  Scheurer-Kestner  and 
Meunier-Dollfus  found  that  the  heating  power  as  determined  by 
the  Favre  and  Silbermann  calorimeter  was  notably  higher  than  that 
calculated  from  the  analysis  by  means  of  the  Dulong  formula.  More 
recently  numerous  determinations,  by  diiferent  American  chemists,  of 
the  heating  values  of  various  American  coals,  by  means  of  the  Thomp- 
son calorimeter  or  its  modifications,  showed,  apparently,  that  the  heat- 
ing values  of  these  coals  were  much  less  than  those  calculated  from  the 
analyses.  The  contradictory  results  of  all  these  researches  must  now 
be  set  aside  in  view  of  the  work  of  Mahler,  in  France,  published  in 
1892,  supplemented  by  the  more  recent  work  of  Lord  and  Haas  in  this 
country  and  by  that  of  Bunte  in  Germany,  all  of  whom  agree  in  show- 
ing that  the  calorimetric  values  and  those  calculated  by  the  Dulong 
formula  from  the  ultimate  analysis  are  nearly  identical,  except  in  the 
case  of  cannel-coal,  lignite,  turf,  and  wood,  which  by  Mahler's  tests 
show  a  calorimetric  value  ranging  from  2  to  12  per  cent  higher  than 
that  calculated  from  the  analysis. 

Mahler's  research  was  made  under  the  auspices  of  the  Societe" 
d'Encouragement  pour  1'Industrie  Rationale,  with  its  financial  assist- 
ance to  the  extent  of  3000  francs,  and  his  report  is  published  as  a 
pamphlet  extract  from  the  Bulletin  of  the  Societe,  of  1892,  occupying 
73  pages  quarto,  with  two  large  plates.  It  is  entitled  "  Contribution 
a  PEtude  des  Combustibles:  Determination  Industrielle  de  leur  Puis- 
sance Calorifique.  Par  P.  Mahler,  Ingenieur  Civil  des  Mines,"  etc. 

The  calorimeter  used  by  Mahler  was  a  modified  form  of  the 
44 calorimetric  bomb"  of  MM.  Berthelot  and  Vielle,  described  in  the 
Annales  de  Physique  et  de  CMmie  in  1881  and  1885.  The  bomb, 
with  its  auxiliary  apparatus,  is  shown  in  the  cut,  Fig.  6  on,  page  95. 
It  is  described  in  detail  in  the  report,  and  the  description  of  a  similar 
bomb,  used  by  Professors  Slosson  and  Colburn  in  their  investigations 
of  Wyoming  coals,  with  the  method  of  operating  it,  is  given  below. 

Mahler's  results  are  shown  in  condensed  form  in  the  table  on  the 
opposite  page. 

Mahler's  formula  gives  the  same  result  as  his  modification  of 
Dulong's  when  0  -f  N  =  3.29  #,  and  higher  results  when  0  -f-  N  is 
greater  than  3.29  $,  but  the  difference  is  small,  less  than  1  $,  until 
O-f  N  becomes  greater  than  10  %.  The  average  results  for  the  several 
classes  of  coals  calculated  by  the  Mahler  formula  are  greater  or  lesa 


TESTS   OF  THE  HEATING    VALUE  OF  COALS. 
HEATING   POWER   OF   COALS.     (P.   MAHLER  ) 


1 

2 
3 

4 
5 
<5 
7 
8 

9 
10 
11 

13 

14 
15 
16 
1? 
18 
19 

20 
21 
22 
23 
24 
25 
26 

27 

28 
29 
30 

32 
33 
34 

35 

36 
3? 
38 

Kind  of  Coal. 

Coal  Dry  and  Free  from  Ash. 

||| 

Composition. 

Healing  power 
Calories. 

C. 

H. 

0  +  N. 

3 

ft! 

J! 

+  206 
-     43 
+      9 
-       4 
-  123 
-     34 
+  113 
+     17 

ANTHRACITE  AND  ANTHRACITIC. 

97  00 

95.3? 
95.24 
92.8(5 
93.46 
91.49 
90.00 
91.46 
92.39 

91.26 
91.  19 
90.11 
90.10 
S9.20 
88.89 
90.03 
87.84 
89  53 

2.20 
1.50 
2.16 
3.0? 
3.12 
3.17 
3.95 
3.78 

4.27 
4.46 
4.38 
4.40 
4.67 
4.84 
4  80 
4.87 
4.84 
5.03 
4.84 

2.43 
3.26 
4.99 
3.48 
5.39 
6.83 
4.59 
3.83 

4.48 
4.35 
5.51 
5.49 
6.14 
6.27 
5.17 
7.30 
5.63 
5.74 
8.64 

8256 
8216 
8121 
8532 
8456 
8203 
8540 

8656 
8756 

8767 
8834 
8574 
87!)7 
8839 
8U39 
8867 
8857 
8667 

8668 

8573 
8598 
8408 
8768 
8431 

i 

8173 
8130 
8528 
8333 
8169 
8653 
8704 

8751 

8817 
8651 
8659 
8651 
8678 
8805 
8559 
8757 
8796 
8382 

8654 
8705 
8524 
8407 
8573 
8979 
8717 

De  la  Mure  (Grand  Couche)  ... 

97.25 
96.83 
94.  81 
96.81 
94.00 
93.29 
89.  ob 

85.92 
86.62 
86.00 
88.0? 
78  49 

Hay-Duong  (Tonkin)  .... 

Kebao 

Commentry  .... 

Blanzy,  Puits  Ste.-Barbe  
1  Grande-Combe,  Puits  Petassas    

Creusot. 

Average  

FAT  AND  SEMI-FAT  (DEMI-GRASSE). 
Demi-grasse,  d'Anzin,  Fosse  St.  Marc.    .  .  . 
Grande  Combe  ....          .... 

+    18 

+    95 
+    61 
116 
-  175 

—    34 

-     80 
-  110 
-     61 

-  285 

-     14 
-     44 
—    49 
-   191 

-f  165 
-f  211 

-f  286 

-  199 
-     79 
+    24 
-     11 

-  102 

Roche-la-Moliere.  
Aniche  .... 

Ronchamp  
'        Lens            ...                .... 

76.77 
80.50 
78.25 
77.15 

Cnrrnaux 

Roclie-la-Moliere.  .  .  .            .... 

Saint  Etienne 

79.16 
80.71 

89.23 
86.52 

Mines  de  Portes  (Gard)  
Average 

FAT  GAS-COALS. 
Bethune  
Lens  .... 

69.59 
69  20 

87.03 

87.26 
85.39 
84.52 
85.66 
88  5? 

5.37 
5.44 
5.58 
5.54 
5.60 
5.72 
6.5? 

7.60 
7.30 
9.13 
9.94 
8.73 
5.72 
9.63 

Firminy.  

67.98 
65.73 
60.04 
68  36 

Montrarnbert  

Wigan,  Lancashire      .   .            ... 

Cannel-coal,  Niddrie.  
Average  

FLAMING  COALS,  LIGNITIC. 
Montoic    ...         .                         .... 

47.00 
62  93 

88.79 

83.95 
84.26 

83.17J 
81.54i 
78.72 

5.64 
5.27 
5.68 
5.64 
5.67 

10  42 
10.46 
11.14 
12.83 
15.61 

8570 
8350 
8270 
8083 
7837 

8371 
8271 
S294 
8072 
7735 

Blanzy  (.Puits  Sie  -Marie) 

68.05 
64.20 
60.61 
58.77 

Decazeville  (Bourran).      ... 

Blanzy  (Puits  Ste.-Eug6nie.  . 

Decazeville  (Tramont) 

Average  

-    74 
-     18 

-  157 
-  299 
-  138 

-  734 

-  400 
-  396 
-  583 

Average  of  above  four  classes  

LIGNITES. 
Terre  de  Feu  

47.23 
49.66 
50.05 

31.07 

71.  01  1 
69.24 
66.36 

57.2l| 
51  08 

5.94 
5.06 
5.01 

5.96 

6.02 

5.88 
6.17 

23.05 
25.71 
28.63 

36.82 

42.90 
43.li9 
49.39 

7039 
6616 
6076 

5903 

4828 
46S9 
4200 

6882 
6317 
5938 

5169 

4428 
4293 
3617 

Trifail  (Styria)  

Vaurigard. 

TURF  FROM  BOHEMIA  .  . 

WOOD. 
Partially  drv,  Sapin  de  Norvege  

Bois  de  Chene  de  Lorraine  
Cellulose.  C19HIOO10  ••      



50.44 
44.44' 

*Dulong's  formula,  slightly  modified  by  Mahler,  is:  <?=]7jn  I  8140C  +  34,500 (H  - 
It  may  be  put  under  the  form  Q-ifa  [8140C  -f  34,500H  -  4312(O-f  N  -1)]. 
Mahler's  own  formula  is  Q  =  TJD  [8140C  -f  34,500H  -  3000(O  +  N)]. 


94  STEAM-BOILER  ECONOMY. 

than  the  calorimetric  results,  as  follows:  Anthracite  and  anthracitic, 
-|-19;  fat  and  semi-fat,  —  34;  fat  gas-coals,  +117;  flaming  coals, 
lignitic,  +42;  average  of  these  four  classes,  +26,  as  compared  with 

—  18,  the  average  difference  between  the  results  calculated  by  the 
modified  Dulong  formula  and  the  calorimetric  result,  as  shown  in  the 
table.    For  the  lignites,  turf,  and  wood,  Mahler's  formula  gives  much 
smaller  differences  than  Dulong's,  viz.:  +102,  +6,  +194,  -294, 
+  119,  +134,  +64,  as  compared  with  —157,  —299,  —138,  —  734, 

—  400,  —396,  —583,  the  figures  in  the  table.     For  all  ordinary  coals, 
therefore,  Dulong's  formula  may  be  considered  the  more  accurate  of 
the  two,  giving  an  average  difference  of  only  18  calories  in  over  8000. 

DESCRIPTION  OF  MAHLER'S  BOMB  CALORIMETER.* 

The  essential  conditions  for  the  determination  of  heat  of  combus- 
tion are  that  the  product  be  completely  burned,  that  the  heat  pasa 
entirely  into  the  water  of  the  calorimeter  vessel,  and  that  the  combus- 
tion be  as  quick  as  possible.  These  conditions  are  best  attained  by  the 
process  devised  by  Berthelot,  according  to  which  the  combustion  takes 
place  in  a  closed  steel  vessel  (the  so-called  bomb)  filled  with  oxygen 
under  twenty  to  twenty-five  atmospheres  pressure  and  almost  entirely 
immersed  in  the  water  of  the  calorimeter.  Under  these  circumstances 
a  hydrocarbon  burns  completely  to  carbon  dioxide  and  water  in  a  few 
seconds,  none  of  the  products  of  combustion  can  escape  and  the  heat 
passes  into  the  surrounding  water  in  the  course  of  two  or  three 
minutes.  The  high  price  of  Berthelot's  calorimeter,  about  $1,500,  has 
prevented  it  from  coming  into  common  use.  In  June,  1892,  an 
account  was  published  of  a  modification  of  Berthelot's  apparatus  in- 
vented by  M.  Mahler  in  which  the  expensive  platinum  lining  of  the 
bomb  was  replaced  by  a  thin  coating  of  enamel  without  impairing  the 
efficiency  of  the  instrument.!  A  calorimeter  of  this  kind  was  pro- 
cured by  the  University  of  Wyoming  in  July,  1894,  for  the  study  of 
the  coal  and  petroleum  of  the  State  and  for  use  in  food  investigations 
in  the  Agricultural  Experiment  Station. 

The  bomb  (B  in  cut)  of  our  apparatus  is  15  cm.  high  and  10  cm. 
in  diameter,  with  an  average  thickness  of  8  mm.  It  is  Martin-Sie- 

*Frora  an  article  on  "The  Heating  Power  of  Wyoming  Coal  and  Oil."  by 
Professors  E.  E.  Slosson  and  L.  C.  Colburn,  published  in  a  special  Bulletin  of  the 
University  of  Wyoming,  Laramie,  Wyo.,  January,  1895.  Another  description 
will  be  found  in- Mahler's  paper  on  "  The  Calorific  Power  of  Combustibles  "  (Bul- 
letin de  la  Societe  d'Encouragement  pour  1'Industrie  Nationale,  Paris,  1892),  and 
in  Poole's  "  Calorific  Power  of  Fuels  "  (John  Wiley  &  Sons,  New  York,  1898). 

\  The  apparatus  is  constructed  by  M.  L.  Golaz,  Rue  Saint-Jacques,  Paris,  and 
is  sold  at  the  following  prices:  Mahler's  calorimeter  complete  750  francs,  pump 
for  compressing  oxygen  500  francs,  pair  of  thermometers  50  francs.  Our  instru- 
ment was  procured  through  Eimer  and  Amend,  New  York. 

A  cheaper  form  of  the  bomb  calorimeter,  which  dispenses  with  pump  or  gas- 
cylinder,  is  described  in  Hempel's  Gas  Analysis. 


TESTS  OF  THE  HEATING    VALVE  OF  COALS. 


95 


mens  soft-forged  steel  of  a  resistance  of  50  kilogs.  per  sq.  mm.  of 
section  (about  70,000  Ibs.  per  sq.  in.),  and  20#  elongation.  It  is 
nickel-plated  on  the  outside  and  coated  on  the  inside  with  a  thin  white 
enamel  to  prevent  corrosion  by  the  oxygen  and  the  acids  which-  are 
among  the  products  of  combustion.  The  capacity  of  the  bomb  is 
580  cc.  A  platinum  tray  (C),  of  30  mm.  in  diameter  and  5  mm.  in 
depth,  is  suspended  from  the  cover  by  a  rod  of  platinum.  A  similar 
rod  passing  through  the  cover,  but  insulated  from  it,  readies  nearly  to 
the  tray  and  serves  as  the  other  electrode.  The  cover  is  screwed  on 


FIG.  6. — MAHLER'S  BOMB  CALORIMETER. 

A,  water-jacket  ;  B,  bomb  of  enamelled  steel  :  C,  platinum  tray  ;  D,  calorimeter* 
vessel  ;  E,  electrode  ;  f,  iron  wire  for  ignition  ;  G,  support  for  stirring- 
apparatus  ;  7T,  stirring-mechanism  ;  L,  lever  for  stirring;  M,  manometer; 
0,  cylinder  of  oxygen  ;  S,  stirring-apparatus  ;  T,  thermometer ;  Z,  clamp. 

over  the  top  of  the  bomb  and  a  hermetical  joint  secured  by  a  ring  of 
lead.  The  oxygen  is  passed  in  through  the  stem  of  the  needle-valve, 
which  is  screwed  down  when  the  bomb  is  rilled.  The  bomb  is  set  in  a 
support  which  touches  the  bottom  of  the  calorimeter  vessel  on  three 
points.  The  calorimeter  vessel  is  a  pail  of  thin  brass,  23  cm.  high  and 
14  cm.  diameter.  This  rests  on  three  points  of  a  light  wooden  support, 
and  is  surrounded  by  a  large  double-walled  vessel,  covered  with  thick 
felt,  containing  water  at  the  normal  temperature  of  the  room.  An 
ingenious  stirring  mechanism  enables  one  to  keep  the  water  of  the 
calorimeter  in  thermal  equilibrium  with  slight  effort.  The  calorimeter 
is  so  well  isolated  from  external  influences  that  the  water  often  doea 


96  STEAM-BOILER  ECONOMY. 

not  vary  in  temperature  .01°  in  fifteen  minutes,  although  the  air  of 
the  room  may  be  quite  variable. 

Two  thermometers  were  used,  one  reading  between  8°  and  18°  C., 
and  the  other  between  18°  and  28° ;  each  degree  covering  a  space  of  3^- 
«cm.  They  are  graduated  to  ?V°»  and  were  read  to  0.01°,  although 
with  a  glass  they  can  be  read  to  a  much  finer  interval. 

The  oxygen  used  was  made  in  the  laboratory,  purified  by  passing 
through  a  solution  of  caustic  potash  and  three  rolls  of  copper  gauze, 
and  kept  in  gas-bags;  the  slight  correction  indicated  for  Berthelot  for 
the  loss  of  heat  through  vaporization  of  water  has  not  been  applied. 

THE   PROCESS   OF   COMBUSTION. 

One  gram  of  the  coal  or  oil  is  weighed  into  the  tared  platinum 
tray,  which  is  then  attached  to  the  platinum  rod  in  the  calorimeter- 
bomb.  A  piece  of  iron  wire  of  known  weight  is  stretched  across  from 
the  rod  supporting  the  tray  to  the  insulated  support,  and  preferably 
touching  the  combustible  or  buried  in  it.  The  bomb  is  then  placed  in 
a  lead-lined  clamp,  and  the  top  tightly  screwed  on  by  means  of  a 
wrench.  The  needle-valve  is  opened  and  connected  with  the  com- 
pression pump  by  a  long  slender  copper  tube.  Oxygen  is  then  forced 
into  the  bomb  until  the  manometer  reads  20  or  25  atmospheres.  The 
needle-valve  is  closed  and  disconnected  from  the  filling  tube,  and  the 
bomb  is  immersed  in  the  water  of  the  calorimeter.  The  water  should 
be  2°  to  3°  lower  in  temperature  than  the  air  of  the  room  and  the 
water  in  the  jacket  of  the  calorimeter,  and  a  sufficient  amount  should 
be  weighed  out  to  cover  the  bomb  nearly  to  the  top  of  the  insulated 
electrode.  In  our  instrument  2309  grams  of  water  was  usually  taken, 
as  that  gave  with  the  water  value  of  the  apparatus  (491  grams)  a 
convenient  factor  for  calculation.  The  stirring  apparatus  is  kept  in 
motion,  and,  as  soon  as  the  change  in  temperature  becomes  constant, 
readings  of  the  thermometer  are  taken  at  intervals  of  one  minute.  At 
the  end  of  the  fifth  minute  the  combustible  is  fired  by  passing  an  elec- 
tric current  through  the  iron  wire,  raising  it  to  redness.  We  used  a 
plunge  battery  of  six  bichromate  cells  for  this  purpose.  One  wire  is 
connected  to  the  insulated  electrode,  and  the  other  is  touched  to  some 
exposed  part  of  the  bomb.  In  about  ten  seconds  the  thermometer  is 
observed  to  rise,  rapidly  at  first,  then  more  slowly,  reaching  a  maxi- 
mum usually  on  the  second  or  third  minute  after  firing.  After  the 
maximum  it  falls  regularly  and  slowly  if  the  proper  temperature  has 
been  chosen  for  the  water,  and  readings  are  again  made  at  intervals  of 
a  minute  for  five  minutes  more.  Then  the  bomb  is  taken  out  of  the 
calorimeter,  the  needle-valve  cautiously  opened  to  allow  the  products 
of  combustion  and  residual  oxygen  to  escape ;  after  which  the  bomb  is 
opened  and  rinsed  out  with  distilled  water.  The  rinsings  are  titrated 
with  a  standard  solution  of  potassium  hydrate  or  sodium  carbonate  to 
determine  the  amount  of  nitric  acid  formed  by  the  combustion;  and, 
if  the  combustible  contains  sulphur,  the  solution  is  set  aside  for 
determination  of  sulphuric  acid.  The  whole  operation,  including  the 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  97 

weighing  of  the  sample  and  pumping  in  the  oxygen,  can  be  completed 
in  less  than  an  hour  if  everything  works  well. 

Multiplying  the  weight  of  water  taken  plus  the  water  value  of  the 
apparatus  by  the  corrected  rise  in  temperature  gives  the  heat  of  com- 
bustion of  one  gram  of  the  substance,  subject  to  the  corrections  men- 
tioned below. 

CORRECTIONS. 

1.  Correction  for  the  Influence  of  the  Temperature  of  the  Environ- 
ment. —  This  is  the  largest  and  most  important  correction  to  be  made, 
although  on  account  of  the  short  interval  during  which  the  tempera- 
ture rises  —  usually  two  minutes  —  it  is  smaller  in  this  process  than  in 
any  other. 

As  there  is  no  way  of.  measuring  directly  the  amount  of  heat  lost  or 
gained  by  the  calorimeter  from  the  moment  of  firing  to  the  moment 
when  all  the  heat  of  combustion  has  been  given  up  to  the  water  sur- 
rounding the  bomb,  it  is  necessary  to  calculate  this  from  the  rate  of 
change  of  temperature  before  firing  and  the  rate  of  change  when  the 
temperature  has  come  again  to  equilibrium.  This  correction  is  most 
accurately  given  by  the  application  of  the  Regnault-Pfaundler  formula. 
If  the  preliminary  period  and  the  final  period  are  each  five  minutes, 
with  readings  of  the  thermometer  every  minute,  the  correction  accord- 
ing to  this  formula  is  : 


where  t  indicates  the  temperature  at  the  end  of  the  minute  designated 
by  the  subscript;  ts  is  the  instant  of  firing;  N  is  the  number  of  the 
maximum  reading;  tM  is  the  average  of  the  five  readings  before 
firing  ;  T  is  the  average  of  the  readings  of  the  final  period  ;  D  is  the 
average  change  in  temperature  during  the  final  period,  and  d  is  the 
average  change  in  temperature  during  the  preliminary  period. 

As  in  practice  the  maximum  temperature  nearly  always  occurs  on 
the  seventh,  the  eighth,  or  the  ninth  minute,  the  formula  can  be 
reduced  for  these  three  cases  to  the  following  forms,  which  are  easy  to 
calculate  : 

When  the  maximum  is  the  end  of  the  seventh  minute  the  correc- 
tion for  the  loss  or  gain  of  heat  during  the  minutes  5-6  and  6-7  is 

1  f  [(2*.  +  *,)-  (8*.  +  f.)]  [(*,  +  tt)  -  (t,  +  t,  ,)] 

«l  (<i.  +  M-('.  +  <T~ 

When  the  maximum  is  the  eighth  minute  the  loss  or  gain  for  the 
minutes-  5-6,  6-7,  7-8  is 


$8  STEAM-BOILER  ECONOMY. 

"When  the  maximum  is  the  ninth  minute  the  loss  or  gain  for  the 
minutes  5-6,  6-7,  7-8,  8-9  is 


lo  5) 


This  correction  becomes  a  minimum  when  the  temperature  before 
firing  is  rising  about  three  times  as  fast  as  it  falls  after  the  maximum. 

As  the  .  period  of  combustion  is  so  short  M.  Mahler  has  given  a 
method  of  correction  based  on  Newton's  law  which  gives  results  suffi- 
ciently exact  for  technical  work.  His  rules  are: 

1.  The  law  of  decrease  of  temperature  observed  after  the  maximum 
represents  the  loss  of  heat  before  the  maximum  and  for  any  given 
minute,  on  condition  that  the  mean  temperature  of  this  minute  does 
not  differ  more  than  one  degree  from  the  maximum  temperature. 

II.  If  the  temperature  of  the  given  minute  differs  by  more  than 
one  degree  but  less  than  two  degrees  from  that  of  the  maximum,  the 
number  that  represents  the  law  of  decrease  at  the  moment  of  the  maxi- 
mum less  0.005  will  give  the  desired  correction. 

A  comparison  of  the  two  methods  in  some  twenty  cases  showed  an 
average  difference  of  0.0013,  which  on  one  gram  naphthalene  would 
amount  to  about  three  calories,  or  03.  per  cent;  a  difference  within 
the  limit  of  error  in  technical  work. 

2.  Correction  for  Formation  of  Nitric  Acid.  —  About  fifty  milli- 
grams of  nitric  acid  are  formed  from  the  nitrogen  of  the  air  by  the 
combustion,  and  it  is  necessary  to  ascertain  the  amount  of  this  and 
subtract  the  heat  of  formation,  227  cal.  per  gram,  from  the  heat  of 
combustion  of  the  substance  under  examination.     This  is  estimated 
by  titration  with  a  standard  alkali  solution  containing  3.706  grams  of 
sodium  carbonate,  Na2C03.     One  cubic  centimeter  of  this  solution  is 
equal  to  .0044  gram  nitric  acid,  of  which  the  heat  of  formation  is  one 
calorie,  so  the  number  of  cubic  centimeters  required  to  titrate  the 
washings  of  the  bomb  can  be  written  at  once  as  calories.     Methyl 
orange  is  used  as  an  indicator. 

3.  Correction  for  the  Combustion  of  the  Iron  Wire.  —  The  combus- 
tion of  the  small  piece  of  iron  wire  used  to  ignite  the  combustible  adds 
to  the  apparent  rise  in  temperature,  and  correction  must  be  made  by 
taking  a  known  weight  of  wire  and  subtracting  its  heat  of  combustion. 
A  No.  32  to  36,  Brown  and  Sharpe  gauge,  is  suitable,  and  it  is  prefer- 
able to  use  the  copper-plated  wire,  as  the  plain  wire  easily  becomes 
oxidized  on  the  surface.     Of  No.   36  wire  one  meter  weighs  .3160 
gram  ;  of  this  in  our  experiments  we  used  a  length  of  4.8  centimeters, 
giving  a  heat  of  combustion  of  25  calories. 

The  heat  of  combustion  of  iron  under  these  circumstances  is  stated 
to  be  1650  cal.  per  gram.*  This  is  on  the  assumption  that  all  the 
iron  is  burned  to  Fe304.  That  this  is  not  correct  is  shown  by  the 

*Berthelot:  Traite  Pratique  de  Calorimetrie  Cliimique,  p.  139. 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  99 

following  analyses  of  the  iron  oxide  resulting  from  some  twenty  com- 
bustions each:  No.  1,  71.59  per  cent  iron  in  oxide;  No.  2,  75.81  per 
cent  iron  in  oxide.  The  first  would  correspond  to  74.7  per  cent 
Fe304  and  25.3  per  cent  Fe208,  while  the  second  might  be  composed 
of  86.8  per  cent  Fe304  and  13.2  per  cent  unburned  iron.  Other 
mixtures  of  iron  and  its  oxides  would  of  course  give  the  same  analyt- 
ical results.  The  heat  of  combustion  of  ferric  oxide  is  not  exactly 
known,  but  it  is  certainly  less  than  that  of  Fe304.  It  appears  from 
this  that  the  character  of  the  oxides  formed  is  variable  and  the  ordi- 
nary correction  consequently  inaccurate  by  several  calories.  The  error 
is  not,  however,  as  great  as  the  analyses  would  seem  to  indicate,  for  it 
was  only  the  larger  particles  such  as  could  be  easily  picked  off  that 
were  taken  for  analysis. 

4.  Correction  for  Sulphur. — The  presence  of  sulphur  in  the  com- 
bustible necessitates  another  correction,  for  the  free  sulphuric  acid 
formed  by  the  combustion  of  sulphur  compounds  will  be  titrated  as 
nitric  although  its  heat  of  combustion  is  different  and  the  heat  of  the 
burning  sulphur  is  a  legitimate  part  of  the  heat  of  combustion  of  the 
fuel.  The  sulphuric  acid  must  therefore  be  determined  in  the  rins- 
ings of  the  bomb  after  the  titration  for  free  acid,  and  the  heat  of  for- 
mation of  its  equivalent  in  nitric  acid  subtracted  from  the  number 
obtained  by  titration.  The  weight  of  barium  sulphate  multiplied  by 
100  gives  directly  the  number  of  calories  to  be  subtracted. 

Sulphur,  however,  exists  in  coal  in  three  forms:  organic  sulphur 
compounds,  pyrites,  and  sulphates,  chiefly  gypsum.  Of  these  thft 
third  at  least  would  not  be  converted  into  free  acid  by  the  combustion, 
and  the  ordinary  correction  would  be  too  great.  The  point  is  of  espe- 
cial importance  in  dealing  with  Wyoming  coals,  for,  although  the  per- 
centage of  sulphur  is  generally  small,  yet  it  is  more  often  in  the  form 
of  gypsum  than  pyrites.  Nevertheless,  as  to  find  the  original  state  of 
the  sulphur  would  require  two  analyses,  the  whole  is  regarded  as 
forming  sulphuric  acid,  and  the  equivalent,  usually  amounting  to  about 
5  cal.,  has  been  subtracted  in  all  cases. 

DETERMINATION"  OF  WATER  VALUE  OF  THE  APPARATUS. 

The  heat  produced  by  combustion  is  absorbed  not  only  by  the 
water  in  the  calorimeter,  but  also  by  the  calorimeter  vessel,  the  bomb, 
the  stirring  apparatus  and  thermometer  in  contact  with  it.  But  the 
amount  of  heat  absorbed  by  them  depends  on  their  weight  and  mate- 
rial. It  is  therefore  necessary  to  find  the  water  value  of  the  apparatus, 
that  is,  what  weight  of  water  would  absorb  the  same  amount  of  heat 
for  the  same  rise  in  temperature.  This  is  done  by  multiplying  the 
weight  of  the  different  parts  of  the  apparatus  by  the  specific  heat  of 
the  material  of  which  they  are  composed.*  In  this  case  the  calcula- 
tion was  as  follows: 

*  The  weight  of  the  enamel  on  the  bomb  was  not  known.  The  water  value  of 
the  apparatus  as  calculated  is  therefore  too  low. 


100  STEAM-BOILER  ECONOMY. 

Calorimeter  vessel  445  g.,  stirring  apparatus  143  g.,  588  g. 

brass  X  .093 , 54.69 

Bomb,  3920  g.  steel  X  .1097 430.03 

22.36  g.  platinum  X  .0324 72 

8  g.  lead  X  .031 25 

Thermometer,  bulb  2.72  g.,  tube  33.56  g.,  £  immersed,  8.61 

g.  glass  X  .184 1.58 

35.36  g.  mercury  X  .033 1.17 

Oxygen,  (20  atmospheres  pressure)  16.7  X  .155  * 2.59 

Water  value 491.03 

Another  method  of  determining  the  water  value  of  a  calorimeter 
is  to  burn  in  it  certain  compounds  whose  heat  of  combustion  is  accu- 
rately known.  This  has  the  advantage  that  the  water  value  of  the 
whole  apparatus  is  determined  directly  and  under  the  same  conditions 
as  in  an  ordinary  combustion,  but  it  has  the  disadvantage  that  the 
heat  of  combustion  of  no  compound  is  exactly  known.  In  determin- 
ing the  water  value  of  our  calorimeter  we  made  twelve  combustions 
with  resublimed  naphthalene,  of  which  the  heat  of  combustion  as  de- 
termined by  Berthelot  and  his  assistants  is  9692  calories.  The  aver- 
age of  the  twelve  combustions  gave  491.4  grams  as  the  water  value  of 
the  calorimeter.  One  combustion  with  granulated  sugar,  using  2  gm. 
and  taking  the  heat  of  combustion  as  3961.7  cal.  per  gram,  gave  491  g. 
as  the  value.  As  all  these  are  in  satisfactory  agreement,  the  number 
491  has  been  adopted  as  the  water  value.  A  difference  of  one  gram 
in  water  value  makes  a  difference  of  about  .03  per  cent  in  the  final 
result. 

An  Example. — The  method  of  calculating  the  heat  of  combustion 
may  be  made  more  clear  by  giving  in  detail  an  example  in  which  the 
corrections  are  unusually  large. 

Coal  No.  33.     L.  R.  Meyer,  Carbon.     November  30,  1894. 
1  gram  coal.     .0250  g.  wire.  2300  g.  water  in  calorimeter. 

Preliminary  Period.  Combustion  Period.  Final  Period. 

0_i  l .  47°  C.  5—1 1 . 48°  C.                      9—1 3. 64°  C. 

1—11.47  51—12.50  10—13.63 

3—11.48  6—13.34  11—13.62 

4—11.48  7—13.63  12—13  62 

5—11.48    Fired.  8—13.64  13—13.62 

9—13.64  14—13.61 

Nitric  acid  =  9.0  c.c.  Sodium  carbonate  solution  =  9  cal.  Weight  BaS04, 
.0472. 

From  the  9th  to  the  14th  reading  .03°  heat  was  lost,  or  .006°  per 
minute.  Then  for  the  three  and  a  half  minutes,  5-^-6,  6-7,  7-8,  8-9, 
the  total  loss  =  .021°.  The  temperature  rose  .01°  during  the  prelim- 
inary period,  or  .002°  per  minute.  The  correction  for  the  half-minute 
is  therefore  .001.  The  total  rise  in  temperature  is  from  11.48° 

*  Specific  heat  at  constant  volume. 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  101 

-to  13.64°,  or  2.16°;  adding  to  this  the  correction  .02°  gives  2.18°  for 
the  true  rise  due  to  combustion.  The  water  value  of  the  apparatus, 
49  L  g.,  added  to  the  weight  of  water  used,  2300  g.,  gives  2791  g., 
which  multiplied  by  2.13  gives  6084.4  calories.  The  weight  of  the 
barium  sulphate  with  the  decimal  point  moved  two  places  to  the  right 
gives  4.7  to  be  subtracted  from  9.0  cal.,  leaving  4.3  cal.  The  weight 
of  the  wire,  .0250  g.,  multiplied  by  1650  gives  41.2  cal.  The  sum  of 
the  corrections  for  formation  of  iron  oxide  and  nitric  acid,  45.5, 
subtracted  from  6084.4  gives  6039  calories  for  the  true  heat  of  the 
combustion  of  one  gram  of  the  coal.  The  use  of  Regnault's  formula 
in  this  case  would  make  the  rise  of  temperature  2.179°  and  the  heat 
of  combustion  6036  cal. 

NOTES   ON    CALORIMETEY. 

The  use  of  a  cylinder  of  oxygen  under  great  pressure,  such  as  is 
now  in  the  market,  dispenses  with  a  compression-pump,  and  shortens 
the  time  required  for  a  combustion  by  one-half.  It  has  the  disadvan- 
tage that  the  quality  of  the  oxygen  is  not  as 'much  under  control  as 
where  it  is  made  in  the  laboratory. 

It  is  not  necessary  that  the  coal  should  be  finely  powdered,  nor  is 
there  any  difficulty  in  using  fine  samples.  Of  the  samples  used,  one 
was  in  coarse  fragments  and  some  had  been  passed  through  a  hundred- 
mesh  sieve.  In  using  very  fine  coal  or  freshly  sublimed  naphthalene, 
it  is  convenient  to  compress  it  into  tablets  with  a  "diamond  mortar" 
such  as  is  used  in  crushing  minerals  for  analysis. 

The  cylinder  of  the  compression-pump  must  be  kept  cool  by  a 
water-jacket,  or  the  oil  will  become  ignited  by  the  compressed  oxygen 
and  an  explosion  result. 

The  rapidity  with  which  the  heat  is  given  up  to  the  water  of  the 
calorimeter  is  shown  by  the  following  average  of  ten  determinations : 

Heat  given  off  during  the  period  5-5^  =  27.9  per  cent 

"       "        "         "        "       5i-6  =  50.8    "      " 
«        «       «        «<         «        «        g_7  _  20.1    "      '< 

' 


100.0 

That  is,  78.2  per  cent  of  the  total  heat  is  absorbed  by  the  water  dur- 
ing the  first  minute  and  98.3  per  cent  during  the  first  two  minutes. 

Care  must  be  taken  to  scrape  off  the  iron  oxide  from  the  electrodes 
before  attaching  'the  new  wire,  as  a  very  thin  film  will  prevent  igni- 
tion by  the  electric  current. 

Lord  and  Haas's  Tests  of  American  Coals. — In  1897  Professors 
N.  W.  Lord  and  F.  Haas,  of  the  Ohio  State  University,  Columbus,  0., 
presented  a  paper  to  the  American  Institute  of  Mining  Engineers 
(Trans.,  vol.  xxvii.  p.  259)  giving  the  results  of  proximate  and 
ultimate  analyses  and  determinations  of  calorific  value,  by  means  of 


102  STEAM-BOILER  ECONOMY. 

the  Mahler  calorimeter,  of  forty  different  samples  of  coal,  selected 
from  seven  different  mining  regions.  .Prof.  Lord  also  published  a 
paper  in  Engineering  News  of  Feb.  16,  1899,  giving  the  results  of 
similar  tests  of  five  samples  of  coal  from  different  parts  of  Jackson 
Co.,  Ohio.  The  figures  obtained  in  both  series  of  tests  are  given  in 
the  table  on  pages  104  and  105.  The  figures  in  the  last  two  columns 
have  been  calculated  by  the  author,  to  show  the  heating  value  and  the 
per  cent  of  fixed  carbon  of  the  combustible,  which  were  not  given  in 
the  original  papers.  The  ultimate  analyses  as  reported  include  the  hy- 
drogen and  oxygen  of  the  moisture,  together  with  that  of  the  dry 
coal,  and  the  figures  for  "average,  dry  coal,"  have  been  computed  by 
the  author  in  order  to  make  the  analyses  comparable  with  analyses  of 
other  coals. 

These  tests  are  by  far  the  most  complete  that  have  up  to  this  time 
been  made  of  American  coals.  The  extreme  accuracy  of  the  work  is> 
shown  by  the  close  agreement  of  the  results  with  those  obtained  by 
Mahler  with  foreign  coals  of  similar  composition,  as  well  as  by  the 
correspondence  of  the  calorimetric  determinations  with  the  heating 
value  as  calculated  by  the  Dulong  formula.  The  student  is  referred 
to  the  original  paper  for  a  detailed  statement  of  the  precautions  taken 
to  insure  accurate  work  with  the  calorimeter. 

The  following  is  quoted  from  the  paper: 

"  The  probable  error  of  a  single  calorimeter  determination  from  the 
mean  result  of  a  large  number  was  computed  from  all  the  results  on 
21  samples  of  coal,  on  each  of  which  more  than  one  determination 
was  made.  There  were  50  separate  results  on  the  21  samples.  Com- 
puting the  error  by  the  ordinary  formula  gave  plus  or  minus  20  units, 
or  about  0.3  of  1  per  cent  as  the  probable  error  of  one  determination. 
These  results  were  obtained  by  different  observers  and  at  considerable 
intervals  of  time,  and  include  slight  possible  variations  in  the  con- 
dition of  the  sample  as  to  moisture  and  oxidation.  Duplicate  results 
obtained  at  the  same  time  by  the  same  observer  frequently  gave  much 
closer  checks. 

"  The  chemical  analyses  were  made  by  the  ordinary  methods — com- 
bustion with  oxygen  in  a  glass  tube  containing  copper  oxide  and  lead 
chromate  for  the  ultimate  analyses,  while  the  proximate  analyses  were 
made  by  the  methods  used  for  all  the  samples  analyzed  in  this  labora- 
tory for  the  Ohio  Geological  Survey.  In  outline  the  treatment  was 
as  follows : 

"  One  gram  of  the  coal  was  dried  at  100°  to  105°  C.  for  one  hour 
in  a  crucible,  the  loss  being  called  moisture.  After  drying,  the  same 
portion  was  heated  3£  minutes  over  a  Bunsen  burner,  then  3£  minutes 
over  a  blast-lamp,  and  the  loss  was  called  volatile  combustible.  The 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  103 

crucible  was  tightly  covered  arid  not  allowed  to  cool  during  the 
change  from  burner  to  blast-lamp. 

"  The  results  of  the  work  are  given  in  the  following  tables,  in 
which  the  coals  of  each  seam  are  grouped  together.  In  addition  to  the 
analytical  and  calorimetric  data  the  following  figures  are  tabulated: 

"  1.  The  calorimetric  power,  computed  from  Dulong's  formula,  in 
this  form  : 


Cal.  power  =  8080C  +  34,462  (H  -  £0)  +  2250S, 

0,  H,  0,  and  S  being  the  amounts  of  carbon,  hydrogen,  oxygen,  and 
sulphur  in  one  unit  of  the  coal. 

"2.  The  difference  between  this  result  and  the  bomb  determina- 
tion, expressed  in  percentages. 

"  On  examining  the  accompanying  table  of  results,  the  following 
points  appear: 

"  In  the  first  place,  the  remarkable  coincidence  between  the  heating 
powers,  as  calculated  from  Dulong's  formula,  and  the  experimental 
(determinations.  In  the  case  of  the  averages  of  the  different  seams  we 
find  practical  identity  between  the  heating  power  as  calculated  from 
the  formula  based  simply  on  the  heat  developed  by  the  combustible 
elements,  and  the  results  of  the  calorimeter.  This  is  so  much  at  vari- 
ance with  the  claims  of  many  writers  that,  were  it  not  the  result  of  so 
many  determinations,  it  might  pass  as  a  mere  accident.  The  maxi- 
mum difference  between  the  heat  calculated  from  the  elementary 
analysis  and  the  heat  developed  in  the  bomb  is  2  per  cent  of  the  total 
calculated  heat,  the  minimum  difference  0.1  per  cent.  The  possible 
error  of  an  ultimate  analysis  may  be  placed  at  0.5  per  cent  on  carbon 
and  0.2  per  cent  on  hydrogen,  especially  with  coals  as  high  in  ash  and 
sulphur  as  are  many  of  the  samples  included  in  our  tests.  This  would 
lead  to  an  error  of  about  108  units,  or  nearly  1.4  per  cent  on  the  cal- 
culated heat  value.  While,  of  course,  the  probable  error  of  the  ulti- 
mate analysis  is  less  than  this,  it  seems  certainly  possible  that  the  dif- 
ferences between  the  observed  and  calculated  heat  values  are  within 
the  limits  of  experiment. 

"  The  ultimate  analysis  of  coals  is  vastly  more  difficult  to  make  than 
the  calorimeter  determination  ;  and  therefore  it  is  extremely  import- 
ant to  know  how  far  the  ordinary  proximate  analysis  so  universally 
used  in  this  country,  and  so  rapidly  made,  can  serve  as  a  guide  in 
rating  the  calorific  powers  of  coals. 

"  A  relation  between  the  fixed  carbon  and  the  calorimetric  test  was 
stated  by  Mr.  Kent  ("Heating  Value  of  Coal,"  "Mineral  Industry," 
1892,  p.  97);  but  the  results  of  our  work  do  not  appear  to  correspond 
to  his  figures.  Taking  the  Pittsburgh  coal,  we  find  the  average  calo- 
rific power  of  the  samples  observed  to  be  7532.  The  average  ash  is 


104 


STEAM-BOILER  ECONOMY. 


TABLE  OF  RESULTS.     LORD  AND  HAAS'S  TESTS. 


POCAHONTAS   COAL   (SEMI-BITUMINOUS). 


Coal  Dry 

fl> 

3  0- 

^ 

and  Free 

£ 

^  ce 

a 

from 

I 

sl 

8 

Ash. 

Location  of  Mine. 

1 

§ 

« 

^j_J 

PH 

g 

j 

i 

1 

a 
I 

| 

i 

6 

.2 

a 

i 
1 

!I 

$1, 

rence. 

i 

Is 

•O 

T3 

>., 

^ 

Q, 

§D 

eS 

x» 

Q 

o  ^ 

& 

O.™ 

5 

H 

o- 

* 

3 

3 

8 

O 

E 

6 

o~ 

to 

s 

&  y 

Run  of  mine  

83  75 

4  22 

3  36 

85 

57 

7  25 

80 

18  30 

73  fiR 

8062 

8089 

3 

80  10 

K7RS 

60 

8  60 

75 

17.05  73  60 

7915 

81   19  8731 

i>          .. 

85.46 

4.25 

3.24 

.85 

.57 

5.63 

63 

18.6275.12 

8185 

8246 

-   .b 

SO.  14,8732 

(t          (4 

63 

6  99 

61 

17  92  74  48 

8080 

80  61  8745 

it          4i 

85.40 

4.39 

3.94 

.85 

.62 

4.80 

.85 

18.  GO 

75.75 

8281 

8258 

+  -3 

80.2&K77 

Average  

60 

6.65 

73 

18.10  74  r>2 

8105 

80  48  8751 

84.87 

1  °9 

3.51 

59 

.76 

18.51 

74  84 

8-176 

8198 



80.18 

8759 

Average  1-3-5  

8n 

5  89 

"  Dry  Coal. 

85.52 

4.24 

2.85 

.86 

.59 

5.94 

THACKER   COAL,    WEST   VIRGINIA. 


Eun  of  mine  

78.90 

5.14 

6.88 

1.42 

1.16 

6  50 

1.40 

35.00 

57.10 

7768 

7876 

-1.3 

62.00 

8434 

"        "    2d  lot   .... 

1  18 

7.50 

1.60 

34  75  56.15 

7738 

61  77 

85  n 

Nut  Coal 

1  81 

7  30 

1  18 

36  07  i-55  45 

7711 

60  59 

SI  25 

"       "   2dlot  

78.40 

5.19 

7.56 

1.40 

1.40 

6.05 

1.35 

36.35 

56.25 

7867 

7831 

4-  .4 

60.75 

8496 

1  39 

6.84 

1  38 

135.54 

56.24 

7771 

61.28 

8467 

7853 

Average  11-14  

78.65 

5.17 

7.22 

1.41 

1.28 

6.27 

1.38 

35.68 

56.67 

7817 

61.38 

8465 

"  Dry  Coal  . 

79.75 

5.09 

6.07 

1.43 

1.30 

6.  30 

PITTSBURGH  COAL,    ALLEGHENY  CO.,    PENNSYLVANIA. 


77.20 
76.56 
76.57 
73.50 
74.45 
73.91 
74.48 

75.24 
76.30 

5.26 
5.22 
5.13 
5.19 
5.27 
5.15 
5.05 

8.51 
7.00 

8.82 
8.08 
8.02 
8.89 
8.39 

.68 
.67 
.64 
.44 
.60 
.23 
.37 

1.42 
1.60 
1.76 
2  54 
1.80 
1.77 
1.66 

5.93 
7.95 
6.08 
9.25 
8.86 
9.05 
9.05 

.45 

.08 
.07 
.08 
.09 
2.10 
1.75 

1.37 

36.42 
34.  3^ 
37.79 
37.67 
38.91 
36.20 
36.20 

56.20 
56.59 
55.06 
52.00 
51.14 
52.65 
53.00 

7691 
7630 
7765 
7396 
7496 
7354 
7394 

i7717 
7719 
7614 
7436 
7528 
7404 
7433 

-  .3 
-.1.2 
+2.0 
-  .5 
-  .4 

-  '.5 

60.68 
62.14 
59.30 
57.99 
56.79 
59.26 
59.42 

8304 

8378 
8352 
8248 
8324 
8277 
8299 

Turtle  Creek  
Carnegie        

N.  Mansfield  
Turtle  Creek  

Average  
Dry  Coal.... 

5.18 
5.10 

8.24 
7.12 

.51 
1.53 

1.79 

1.82 

8.02 
8.13 

36.80 

53.81 

7532 

7550 



59.39 

8313 

MIDDLE  KITTANNING   (DARLINGTON  COAL),    LAWRENCE  CO.,   PENNSYLVANIA. 


H<  >y  tdale  

77  83 

5  ff> 

9.38 

1.65 

1  57 

4.35 

1  60 

36.40 

57.65 

7785 

7719 

4-  -9 

i  61  .80  8278 

Beavec  Creek  

74.60 

5.  OB 

8.23 

1.401.96 

8.75 

1.50 

34.33 

55.42 

7360 

7460 

-1.3 

61.758201 

Wampum  

77  93 

5  17 

7.95 

1.652.35 

4.95 

0.75 

38.53 

55.77 

i7825 

7787 

+   -5 

159.14 

8256 

Near  Wampum  
Hoytdale  •. 

76.81 

72.78 

5.22 
4.93 

8.52 
10.57 

1.621.18 
1.341.68 

6.65 
8.70 

0.70 
2.70 

36.80 
35.10 

R5.88 

53.50 

7638 

7245 

7663 
7173 

—  .31160.288244 
+1.0(i60.388177 

Wampum  

72.82 

5  ?5 

8.55 

1.33:3.25 

8.80 

9,  85 

37.50 

r-0.85 

7304 

7395 

-1  2 

157.56 

8267 

Clinton               

73  57 

5  14 

10  14 

1  -,'4 

1  86 

8.05 

2.55 

35.60 

53.80 

!7300 

73°0 

-     3 

80.18 

81fift 

1.46 

r^8 

1.81 

36.32 

7494 

7502 

Average  • 

75.19 

5.14 

9.05 

7.18 

54.  C9 

60.09832G 

Dry  Coal.. 

76.58 

5.  as 

7.57 

1.49 

2.02    7.31 

1! 

TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


105 


TABLE   OF   RESULTS.     LORD   AND  HAAS'S   TESTS.— Continued. 


UPPER   FREEPORT   COAL,    OHIO   AND   PENNSYLVANIA. 


Coal  Dry 

OJ 

j_; 

and  Free 

. 

y  cs 

- 

from 

3 

"3 

;o-s 

0 

h 

Ash. 

Location  of  Mine. 

,0 

B 

PH 

>^ 

PH 

g 

a 

j 

6 

5 

£ 

"53 

PM£ 

§ 

2 
i> 

g 

b£ 

fl 

0) 

3 

1+ 

<D 

0 

£ 

cc""1 

c 

0 

as 

| 

•5 

£> 

o 

O, 

.2 

"8 

o> 

t. 

;'£  * 

s 

| 

5-a 

e3 

X 

*j* 

3 

•s 

o 

Q 

"a 

^rf    r^ 

33 

-^ 

0 

H 

0 

* 

02 

^ 

> 

to 

0 

i6 

O 

fa 

0 

East  Palestine  O 

70  58 

\  88 

7  76 

°4 

3  65 

11    R9 

0  8° 

5U  Q8 

5°  65 

7109 

713° 

60  08 

S1  13 

73.23 

5.15 

8.82 

.47 

1.75    9.58 

1.6537.45 

51.32 

73HO 

735-? 

-   .3 

57.81 

8-^57 

Waterford,  O  

74.39 

5.15    7.80 

.40 

3.44    7.82 

1.5537.29 

53.34 

7'459 

7529 

—     9 

58.85 

S'^30 

Yell»\v  Creek,  O  
tSieubenville,  O  
Cambridge,  O  

73.154.98    7.41 
74.735.26    8.06 
70.6lt5.19  10.33 

.40 
1.44 
.44 

3.89   9.17 
2.85    7.66 
3.01    9.42 

1.2338.72 
1.4739.23 
2.43  37.79 

50.88 
51.54 
50.36 

7464 
7504 

70S8 

7393 
7567 
7116 

t'i 

-    .4 

56.79 

56.78 
57.13 

8330 

8267 
8041 

Steubeiiville,  O  

71.40 

4.62  10  68 

.20^3.00    9  10 

2  40  39  20 

49  30 

7113 

6'*70 

19  0 

55  71 

^037 

Salineville,  O  

72.62 

5.13    9.92 

.23 

3.00   8.10 

2.8036.30 

52.80 

7271 

7276 

-    .1 

59.26 

K160 

71  °9 

5  00    9  28 

34 

2  64  10  45 

2  15  36  70 

50  70 

7277 

'1  3fi 

1  °  0 

New  Galilee,  Pa  

73.57 

5.20    8.94 

.85 

2  24   8.70 

2.3036,70 

52  '30 

7401 

--1.8 

58  76 

Slfir> 

Palestine,  O  

73.64 

5.06    9.47 

.24 

2.34   8.25 

2.45  36.60 

52.70 

7344 

7340 

+  -1 

59.01 

8224 

Average         .... 

72  65 

5  06    8  95 

31 

•'  80 

9.10 
9.28 

1.93 

37.35 

51.63 

7293 

7292 

.... 

58.02 

8197 

"       Dry  Coal..  .  . 

74.09 

4.94    7.37 

.37 

2.95 

I 

MAHONING    COAL. 


Salineville  O 

71.13 
73.44 

4  95 
4.75 

9.93 
7.36 

1.23 
1.27 

1.86  10.90 
1.92,11.26 

3.15 

35.00 

50.95 

7032 

1068 

-   .5 

£9.26 

8182 

Dry  Coal. 

JACKSON   CO  ,    OHIO. 


Center  
Xorth  

70.05 
71.20 
70.12 
71.42 
70.79 

5.43 
5.50 
5.49 
5.37 
5.55 

17.09 
17.71 
16.96 
19.49 
18.60 

1.49 
1.45 
1.50 
1.43 
1.46 

1.47 
1.60 

1.84 
0.76 
1.45 
0  64 
0.95 

1.13 
1.23 

4.10 

3.38 
4.48 
1.65 
2.65 

8.26 
8.45 
7.02 
8.65 
8.50 

8.17 

35.15 
34.09 
37.66 
34.30 
37.75 

35.79 

52.49 
54.09 

50.82 
55.40 
51.10 

52.78 

6854 
6937 
6956 
6981 
7069 

6835 

68(.H) 
•i860 
6795 

6854 

-0.3 
-0.7 
-1.3 

-2.7 
-3.1 

1 
59.89 
61.35 
57.42 
61.76 
57.51 

7821 

7868 
7860 
7783 
7946 

7856 

South  
West  ,  

East  

Average  
Dry  Coal... 

70.72 
77.00 

5.47 
4.97 

17.97 
11.66 

3.25 
3.54 

6953 

6847 

59.59 

MIDDLE  KITTANSING   (HOCKING   VALLEY   COAL),    OHIO. 


69.42 

5.35 

16.27 
15.57 

1.46 
i!43 

1.87 
1.03 
1.67 
1  50 

5.83 
10.101 
9.67 
10.53 
8.50 

6.72 
6.45 
6.65 
6.34 
6.40 

37.13 
36.60 
34.14 
35  18 
36  .  05 

••tf.82 
35.77 

50.3, 

46.S5 
49.51 
47.9"> 
49.05 

6882 
6603 
IS49C 

(51S-J 
6610 

6790 
6520 
^740 

'"• 

-T.9 

57.54 
56.14 
59.20 
57.68 
57.64 

58.12 
58.16 

7870 
7913 
7762 
7797 
7767 

7822 

2d  sample. 

Run  of  mine  

66.50 

5.16 

Lump,  3d  sample  

68.18 

5.36 

15.09 

1.44 

1.43 

Average  

15.61 
10.47 

1.44 

1.54 

1.58 

1.59 
1.70 

8.93 

8  00 
8.57 

6.51 
6.5!) 

48.74 
49.64 

6612 
6663 

6083 

I 

Average  6-8-10  
"Dry  Coal 

68.03 
72.84 

5.29 

4.88 

7800 

106  STEAM-BOILER  ECONOMY. 

8.02,  the  average  moisture  1.37.  Calculating  from  this  the  calorific 
power  of  the  coal  free  from  ash  and  moisture,  we  find  it  to  be  8313. 
The  average  fixed  carbon  is  53.95,  and  this,  calculated  ash-  and  mois- 
ture-free, gives  59.54.  Interpolating  from  Kent's  table,  this  would 
give  8054  as  the  calorific  power,  a  difference  of  259  units,  or  3.2  per 
cent.  The  same  calculation  on  the  average  Freeport  coal  shows  a 
difference  of  296  units,  or  nearly  4  per  cent. 

"  The  determination  of  fixed  carbon  is  very  uncertain,  being  much 
influenced  by  slight  changes  in  method;  therefore  it  is  entirely  possi- 
ble that  these  differences  are  due  to  our  method  of  analysis,  giving  low 
results  as  compared  with  that  used  by  the  chemists  furnishing  his 
figures.  .  .  . 

"  Our  determinations  of  fixed  carbon  could  not  be  used  for  estimat- 
ing the  calorific  power  within  any  satisfactory  limit  of  accuracy. 

"  Attempts  to  derive  a  general  law  for  all  the  coals  examined  were 
abandoned,  and  the  question  was  taken  up,  how  far  the  coal  of  a  given 
deposit  or  seam  can  be  regarded  as  of  uniform  quality,  and  its  specific 
character  determined.  This  has  led  to  the  interesting  results  given 
in  the  tables.  Taking  the  coals  of  the  same  seam,  we  averaged  the 
results  of  the  calorimeter,  and,  reducing  by  the  average  ash  and  moist- 
ure, soon  found  that  comparable  results  were  obtained  by  regarding 
this  value  as  a  constant  for  the  seam  over  the  area  examined." 

"  The  results  of  our  tests  seem  to  indicate  the  interesting  conclusion 
that  the  character  of  a  coal-seam,  as  far  as  its  fuel  value  is  concerned, 
is  a  nearly  constant  quantity  over  considerable  areas.  The  determin- 
ation of  the  value  for  seams  would  be  of  great  use,  as  the  rapid  prox- 
imate analysis,  or,  for  that  matter,  merely  the  determination  of  ash 
and  moisture,  in  low-sulphur  coals,  would  be  sufficient  to  grade  coals 
of  the  same  vein.  Of  course  it  is  dangerous  to  argue  from  so  few  ex- 
amples; but  the  proposition  seems  reasonable.  At  least,  we  hope 
that  further  work  may  confirm  these  conclusions. 

Prof.  Lord  says  concerning  the  Jackson  Co.,  Ohio,  coals: 

"The  failure  of  the  last  two  samples  to  show  close  correspondence 
between  the  calculated  values  by  Dulong's  formula  and  the  calorimetric 
results  is  contrary  to  our  experience  with  other  coals.  These  last  two 
analyses  are  the  average  of  duplicates,  which  do  not  agree  very  satis- 
factorily, and  therefore  the  results  are  open  to  question,  as  I  fear  some 
carbon  may  have  escaped  combustion.  The  other  analyses  are  the 
averages  of  very  closely  agreeing  duplicates.  If  the  conclusion  as  to 
the  comparative  constancy  of  the  heating  value  of  the  combustible  in 
any  given  seam  is  correct,  then  the  determination  of  the  heating  power  of 
any  particular  sample  from  the  seam  becomes  a  simple  matter,  if  the 
ash,  sulphur,  and  moisture  in  the  sample  be  known,  and  the  seam  con- 
stant for  the  kind  of  fuel  be  known." 


TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


107 


The  following  extracts  are  taken  from  a  discussion  of  Lord  and 
Haas's  paper  by  the  author  (Trans.  A.  I.  M.  E.,  vol.  xxvii.  p.  946) : 

The  conclusion  of  the  authors  that  the  actual  coal  (moisture  and 
ash  excluded)  of  a  given  seam  over  considerable  areas  may  be  regarded 
as  of  uniform  heating  value,  is  one  of  great  practical  importance. 
Should  this  conclusion  be  established,  or  its  limitations  denned,  by 
future  tests,  it  will  be  possible  for  us  to  approximate  closely  the  heat- 
ing value  of  any  given  sample  of  coal  by  ascertaining  where  it  is 
mined  and  by  determining  its  moisture,  sulphur,  and  ash,  which  are 
the  three  variable  elements  in  lots  of  coal  from  the  same  mine,  with- 
out going  to  the  expense  of  an  ultimate  analysis  or  a  calorimeter  test, 
In  any  given  mine  or  seam  the  sulphur,  averaged  from  car-load  lots, 
is  reasonably  constant,  especially  in  such  coals  as  are  of  good  repute  in 
the  market  as  steam-coals.  The  moisture  and  ash,  however,  are  sub- 
ject to  accidental  variations,  but  they  are  easily  determined. 

I  have  discovered,  in  the  analyses  given  in  the  paper,  an  interest- 
ing relation  between  the  percentage  of  carbon  as  found  by  the  ulti- 
mate analysis  and  the  percentage  of  fixed  carbon  as  found  by  the  prox- 
imate analysis.  It  is,  that  in  the  bituminous  coals  the  fixed  carbon  is 
nearly  equal  to  the  total  carbon  minus  five  times  the  available  hydro- 
gen (H  —  -JO),  and  that  in  the  semi-bituminous  coal  (Pocahontas)  it 
is  nearly  equal  to  the  total  carbon  minus  three  times  the  available 
hydrogen.  The  following  is  the  calculation  from  the  average  analysis : 

Avail- 
able H. 

Pocahontas 3.89x3=11.67 

Thacker 4.27x5  =  21.35 

Pittsburgh 4.15x5  =  20.75 

Darlington 4.01X5  =  20.05 

Makoning 3.71x5  =  18.55 

Upper  Freeport  ...  3.94x5  =  19.70 

Jackson 3.22x5=16.10 

Hocking  Valley 3.34  X  5  =  16.70 

These  figures  indicate  that  in  the  bituminous  coals  the  volatile 
hydrocarbon  (excluding  H20)  is  equivalent  to  2C2H4-fCH4,  or  to  5 
parts  C  and  1  part  H;  and  that  in  the  semi-bituminous  coals  the 
volatile  hydrocarbon  is  equivalent  to  CH4,  or  3  parts  C  and  1  part  H. 
If  these  relations  should  be  confirmed  by  other  coal  analyses,  they  may 
be  useful  as  a  criterion  of  the  accuracy  of  the  proximate  analysis. 
Also  having  the  ultimate1  analysis  of  a  coal,  and  knowing  its  class,  as 
bituminous  or  semi-bituminous,  the  proximate  analysis  may  be  calcu- 
lated therefrom  with  slight  probability  of  error. 

I  quote  the  following  extracts  from  the  paper: 

"  A  relation  between  the  fixed  carbon  and  the  calorimetric  test 
was  stated  by  Mr.  Kent  ('Heating  Value  of  Coal,'  Min.  Ind.,  1892, 
p.  97);  but  the  results  of  our  work  do  not  appear  to  correspond  to  his 
figures.  .  .  .  Our  determinations  of  fixed  carbon  could  not  be  used 


Differ- 

Fixed 

Differ- 

Total C. 

ence. 

Carbon. 

ence. 

84.87 

73.20 

74.84 

+  1.64 

78.65 

57.30 

56.67 

-    .63 

75.24 

54.49 

53.81 

-    .68 

75.19 

55.14 

5469 

-    .45 

71.13 

52.58 

50.95 

-  1.6:? 

72.65 

52.95 

51.63 

-  1.32 

70.72 

54.62 

52.78 

-1.84 

68.03 

51.33 

49.64 

-1.69 

108 


STEAM-BOILER  ECONOMY. 


for  estimating  the  calorific  power  within  any  satisfactory  limit  of 
accuracy." 

These  statements  of  the  authors  refer  to  the  curve  which  I  plotted 
from  Mahler's  tests  of  European  coals,  published  in  my  article  in  vol. 
i.  of  "  Mineral  Industry/'  and  to  the  table  which  I  derived  therefrom. 

The  value  of  my  curve  and  table  for  use  in  connection  with  Amer- 
ican coals  having  been  thus  called  in  question,  I  have  been  led  to 
study  the  subject  anew,  with  the  view  of  comparing  the  work  of  the 
authors  with  that  of  Mahler  and  of  learning  whether  or  not  there  was 
any  essential  difference  between  the  American  and  European  coals, 
and  whether  a  curve  plotted  from  tests  of  the  latter  would  be  of  any 
value  when  applied  to  the  former. 

In  Fig.  7  I  have  plotted  a  portion  of  the  curve  derived  from  the  re- 
sults of  Mahler  between  the  limits  of  55  and  63  per  cent  of  fixed  carbon, 
together  with  the  results  obtained  by  Lord  and  Haas  on  coals  lying 


1b.  Calories  per  fc.  Combustible. 

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63   .62       61  .     60       59        5«       57        56        55       5 

C500 


Fixed  Carbon.  Per  cent  of  Combustible., 

FIG.  7.— RELATION  OF  HEATING  VALUE 

TO  PER  CENT  OF  FIXED  CARBON. 

(Tests  of  Profs.  Lord  and  Haas.) 


62      61       60       59      58      57      56      55      54- 
Fixed  Carbon. Percentof  Combustible. 


FIG.  8.  —  RELATION  OF  HEATING  VALUE 
TO  PER  CENT  OF  FIXE^  CARBON. 

(Lettered  points  are  averages  of  Lord 
and  Haas's  tests.  Numbered  points  are 
tests  by  C.  W.  Houghton.) 


within  the  same  limits.  The  dots  and  crosses  represent  the  individual 
tests,  and  the  small  black  triangles  the  average  figures  for  each  class  of 
coal.  Each  class  of  coal  is  surrounded  by  a  boundary  line  showing 
the  extent  of  variation,  or  what  I  call  the  ''  field  "  of  each  coal. 

In  Fig.  8  the  same  portion  of  the  Mahler  curve  is  given,  with  the 
average  results  of  Lord  and  Haas,  together  with  the  results  of  calori- 
meter tests  of  thirteen  different  varieties  of  coal,  which  were  made  for 
me  last  year  by  Mr.  C.  W.  Houghton,  M.E.,  assistant  in  Sibley  Col- 
lege, Cornell  University,  using  the  calorimeter  of  Prof.  R.  C.  Carpen- 
ter, which  is  described  in  the  Transactions  of  the  American  Society  of 
Mechanical  Engineers,  vol.  xvi.,  p.  1040.  The  results  of  these  tests 
were  as  follows  : 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  109 

Coal  Dry  and  Free  from  Ash. 

Fixed  Carbon.     Heating  Value. 

Per  cent.  Calories. 


1.  Yougliiogheny,  Pa 62.6 

2.  Pittsburgh,  Pa 60.6  7890 

3.  Vanderpool,  Ky 61.5  8000 

4.  Brier  Hill,  0 61.8  7890 

5.  Hocking  Valley,  0 57.5  7830 

6.  Big  Muddy,  111 62.5  8080 

7.  Streator,  111 56.2  7890 

8.  Ladd,  111 56.8  8170 

9.  Seatonville,  111 54.7  8060 

10.  Wilmington,  111 57.1  7840 

11.  Mt.  Olive,  111 57.1  7610 

12.  Indiana  block 61.4  7950 

13.  Indiana  lump 55.6  7670 

The  figure  for  Streator  coal  is  the  average  of  five  tests  of  samples 
from  as  many  different  car  loads,  the  range  being  from  7780  to  8000 
calories.  The  figure  for  Big  Muddy  is  the  average  of  two  lots,  which 
varied  170  calories;  and  that  from  Wilmington  is  the  average  of  two 
lots  which  varied  80  calories.  The  other  tests  were  of  only  one  sample 
each. 

The  plotting  of  these  tests  shows  that  they  cover  quite  a  wide  field, 
and  tends  to  confirm  the  conclusion  of  the  authors  that  the  heating 
power  has  no  definite  relation  to  the  fixed  carbon;  but  it  will  be 
observed  that  the  general  trend  of  the  field  of  Houghton's  tests  is  in 
the  direction  of  the  Mahler  line;  that  the  maximum  deviation  of 
any  single  test  from  the  Mahler  line  is  less  than  500  calories, 
or  about  6  per  cent;  and  that  Houghton's  tests  arrange  themselves, 
about  equally  on  each  side  of  the  Mahler  line.  These  tests  were 
simply  commercial  ones,  made  to  check  the  results  of  boiler  tests.  I 
am  inclined  to  believe  that  the  figures  of  heating  value  are  much  more 
reliable  than  those  of  the  percentages  of  fixed  carbon,  for  the  latter, 
as  is  said  by  Profs.  Lord  and  Haas,  is  not  easy  to  determine  with 
accuracy. 

Fig.  7  is  especially  interesting  in  showing  that  each  of  the  six 
classes  of  coals  tested  by  the  authors  of  the  paper,  within  the  limits  of 
55  and  62  per  cent  of  fixed  carbon,  has  a  law  of  its  own.  Four  of 
these  classes,  the  Pittsburgh,  the  Lawrence  Co.,  Pa.,  the  Jackson,  and 
the  Hocking  Valley,  0.,  seem  to  have  a  very  uniform  heating  power 
through  a  wide  range  of  variation  in  percentage  of  fixed  carbon. 
The  same  might  be  said  of  the  Upper  Freeport  coal,  if  the  two  tests 
which  give  less  than  8100  calories  were  omitted.  The  four  samples 
of  Thacker,  WT.  Va.,  coal  are  very  close  together,  both  in  heating 
power  and  in  percentage  of  fixed  carbon. 

In  Fig.  9  are  plotted  all  of  Mahler's  results  between  the  limits  of 
47  and  97  per  cent  of  fixed  carbon.  A  boundary  line  is  run  around 
all  the  tests,  and  the  average  curve  given  in  the  paper  in  "  Mineral 


110 


STEAM-BOILER  ECONOMY. 


'•2    HJ^PM^HO; 

2     <fpq  O  Q~H  fa  cj  TH 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  Ill 

Industry,"  is  reproduced.*  Comparing  the  curve  with  the  plottings 
of  the  individual  tests  and  with  the  boundary  enclosing  them,  it 
will  be  seen  that  they  justify  the  conclusion  stated  in  that  paper, 
viz.,  that,  "knowing  the  percentage  of  fixed  carbon  in  the  dry  coal 
free  from  ash,  we  may,  in  the  case  of  all  coals  containing  over  08  per 
cent  of  fixed  carbon,  predict  their  heating  value  within  a  limit  of 
error  of  about  3  per  cent." 

Fig.  9  shows  also  that  the  figures  for  Pocahontas  coal  obtained  by 
Lord  and  Haas  all  come  remarkably  close  to  the  Mahler  line,  all  five 
tests  lying  entirely  within  the  Mahler  field.  The  average  figure  from 
these  tests,  8751  calories,  is  only  49  calories,  or  less  than  0.6  per  cent, 
lower  than  the  figures  in  my  table  for  80  per  cent  of  fixed  carbon. 

Another  thing  shown  by  Fig.  9  is,  that  Lord  and  Haas's  tests 
cover  only  a  small  portion  of  the  range  of  composition  of  the  coals 
tested  by  Mahler.  Mahler's  tests,  excluding  the  lignites,  cover  the 
entire  range  between  58  and  97  per  cent  of  fixed  carbon,  while 
Lord  and  Haas's  are  confined  between  55.7  and  62.2  per  cent,  ex- 
cept the  five  tesfes  of  Pocahontas  coal,  which  are  between  80.1  and 
81.2  per  cent. 

With  the  three  diagrams,  Figs.  7,  8,  and  9,  we  may  find  what  is 
the  probable  error  of  the  conclusion  that  I  drew  in  1892  from  the 
study  of  Mahler's  work,  viz.,  that  " knowing  the  percentage  of  fixed 
carbon  in  the  dry  coal  free  from  ash,  we  may  in  the  case  of  all  coal 
containing  over  58  per  cent  of  fixed  carbon  predict  their  heating 
value  within  a  limit  of  error  of  about  3  per  cent."  Excluding  the 
coals  that  have  below  58  per  cent  of  fixed  carbon  in  the  combustible, 
the  variation  of  any  one  of  Lord  and  Haas's  coals  from  the  Mahler 
line  does  not  exceed  320  calories,  or  4  per  cent.  Taking  the  average 
figure  for  each  class  of  coals,  it  falls  in  all  cases  within  the  limit  of 
3  per  cent.f  The  figures  from  Hough  ton's  tests  also  fall  within  the 
limit  of  4  per  cent  variation  from  the  Mahler  line,  except  coal  No.  4, 
Brier  Hill,  0.  (of  which  only  one  test  was  made),  which  falls  400 
calories,  or  nearly  5  per  cent,  below  the  Mahler  line. 

On  the  whole,  therefore,  I  consider  that  both  Lord  and  Haas's 
and  Houghton's  tests  are  a  substantial  confirmation  of  the  conclusion 
I  drew  from  Mahler's  tests.  Taking  into  consideration  the  fact  that 
the  reported  percentage  of  fixed  carbon  is  very  apt  to  be  2  or  3  per  cent 
in  error,  I  am  disposed  to  hold  to  my  original  conclusion,  at  least 
until  a  larger  series  of  tests  may  show  that  it  should  be  modified. 

*  The  curve  is  plotted  from  the  figures  given  in  the  table  on  page  48.  The 
average  results  from  coals  of  four  counties  in  Wyoming,  by  Slosson  and  Colburn, 
Lave  been  added  to  the  diagram. 

|  This  was  written  before  the  tests  of  the  Jackson  Co.  coals  were  published. 
Two  out  of  the  five  samples  gave  exceptionally  low  calorimetric  values  as  related 
to  their  fixed  carbon  percentage,  one  of  them  being  6  per  cent  below  the  Mahler 
line,  and  the  average  of  the  Jackson  Co.  coals  is  thus  4  per  cent  below  the  line. 
The  Wyoming  coals,  now  included  for  the  first  time  in  the  diagram  lie  entirely 
outside  of  the  Mahler  field  and  appear  to  belong  to  an  entirely  different  class 
from  any  of  the  Eastern  coals. 


112 


STEAM-BOILER  ECONOMY. 


It  is  to  be  observed,  however,  that  the  Mahler  line  falls  rapidly 
with  percentages  below  6xJ  per  cent  of  fixed  carbon;  and  it  is  there- 
fore to  be  expected  that  below  this  point  there  will  be  a  greater  range 
of  variation  in  heating  value  than  auove  it.  When  the  volatile  matter 
exceeds  38  per  cent,  an  increasing  proportion  of  it  is  oxygen,  and 
the  relative  proportion  of  oxygen  in  the  highly  volatile  coal  varies  ia 
the  coals  of  different  districts,  as  is  shown  by  Lord  and  Haas's  analy- 
ses. Thus  the  Upper  Freeport  coal  averages  only  9.58  per  cent  of  O 
(in  the  coal  dry  and  free  from  ash),  while  the  Hocking  Valley  coal 
averages  16.10  per  cent,  although  both  coals  have  the  same  percent- 
age of  fixed  carbon,  viz.,  58  per  cent.  Full  credence,  therefore,  is  to 
be  given  to  the  conclusions  drawn  from  Lord  and  Haas's  tests,  that, 
when  the  fixed  carbon  is  less  than  62  per  cent  of  the  combustible, 
each  class  of  coal  has  a  law  of  its  own,  and  coals  of  any  one  class  may 
differ  in  heating  power  from  the  coals  of  another  class  containing  the 
same  percentage  of  fixed  carbon  to  an  extent  as  great  as  5  per  cent — 
as  in  the  case  with  the  Upper  Freeport  and  the  Hocking  Valley 
coals.* 

Heating  Value  of  Wyoming  Coals. — The  following  table  is  con- 
densed from  a  report  by  Professors  E.  E.  Slosson  and  L.  C.  Colburn  of 
the  University  of  Wyoming,  Laramie,  Wyo.  (Special  Bulletin,  Jan., 
1895.) 


Coal. 

Combustible. 

Water. 

Volatile 
Matter. 

1  Fixed 
Carbon. 

| 

< 

Sulphur. 

Calories. 

Fixed 
Carbon. 

' 

Calories. 

tJ.0 

^ 

PQa 

Uinta  Co    

2.95 

8.82 

38.00 
33.55 

54.00 

51.75 

4.95 
5.90 



7467 
6017 
6673 

7140 
5375 
6565 

7358 
5949 
6598 

5293 
4966 
4931 

58.70 
60.67 
58.39 

60.72 
52.05 
59.63 

60.12 
55.14 
60.63 

56.38 
56.31 
57.13 

8116 
7055 
7573 

7863 
6567 
7540 

7942 
7120 
7432 

6587 
6326 
6350 

14,609 
12,699 
13,631 

14.15B 

11,821 
13,572 

14,296 
12.816 
13,378 

11,857 
11,387 
11,450 

«       « 

Av.  of  8  

5.80 

4.87 
13.65 
7.83 

5.55 
14.23 

8.65 

13.55 
14.70 
14.50 

36.16 

35.68 
39.25 
35.32 

36.95 

37.48 
34.80 

35.05 
34.30 
33.35 

51.78 

55.15 
42,60 
52.15 

55.70 
46.07 
53.69 

45.30 
44.20 
44.30 

6.26 

4.30 
4.50 
4.55 

1.80 
2.22 
2.71 

6.10 

6.80 
7.85 

0.60 

.77 
.80 
.71 

.86 
.44 
.75 

*.*34 
.42 

«  <        « 

Av.  of  7  

Sweetwater  Co  

Av  of  13  

Johnson  Co  j 
3  samples  1 

*  The  average  heating  value  of  the  Jackson  Co.,  Ohio,  coals  is  about  5|  per 
cent  lower  than  that  of  the  Pittsburg  coals,  both  having  about  the  same  percentage 
of  fixed  carbon  in  the  combustible.  The  lowest  average  value  for  the  Wyoming- 
coals  (Johnson  Co.)  6421  calories,  is  nearly  12  per  cent  below  the  average  of  the 
Upper  Freeport  (Ohio  and  Pa.)  coals,  and  the  difference  between  the  heating  value 
of  the  Johnson  Co.  and  the  Uinta  Co.,  Wyoming,  coals  is  over  15  per  cent  of  the 


Tfib'lS  OF  THE  HEATING    VALUE  OF  COALS.  113 

The  figures  in  the  last  three  columns  have  been  calculated  by  the 
author.  The  figures  in  the  first  two  lines  for  each  of  the  three  coun- 
ties first  named  are  selected  so  as  to  show  respectively  the  coals  of  the 
.highest  and  the  lowest  heating  value  per  pound  of  combustible  of  the 
samples  tested.  They  show  quite  a  large  range  of  variation  within 
the  limits  of  a  county.  The  heating  value  per  pound  combustible  appar- 
ently bears  no  definite  relation  to  the  percentage  of  fixed  carbon  in  the 
combustible,  indicating  that  the  quality  of  the  volatile  matter  is  vari- 
able. Coals  from  Weston,  Natrona,  Albany,  Fremont,  Sheridan, 
Crook,  and  Converse  counties  are  within  the  range  of  quality  of  the 
coals  given  in  the  table. 

The  Mahler  calorimeter  was  used  in  determining  the  heating  values. 

The  Calorific  Power  of  Weathered  Coals. — Messrs.  R.  S.  Hale  and 
Henry  J.  Williams  of  Boston,  in  Trans.  Am.  Soc.  M.  E.,  vol.  xx., 
1898,  p  333,  give  the  results  of  analyses  and  calorimetric  tests  (by 
Mr.  Williams's  bomb  calorimeter)  of  several  coals  which  had  been  ex 
posed  to  the  weather  for  eleven  months,  and  of  duplicate  samples  of 
the  same  coals  which  had  been  sealed  in  glass  jars.  The  results  are 
condensed  in  the  table  on  page  114.  The  following  notes  are  ex- 
tracted from  the  paper : 

For  tests  of  fine  coal  the  samples  were  ground  in  a  coffee-grinder, 
and  thoroughly  mixed  and  divided  into  two  parts.  For  tests  of  lump 
coal  the  coals  were  broken  into  lumps  of  about  nut  size,  and  alternate 
lumps  taken  from  the  pile  to  form  two  samples.  Where  tests  of  both 
fine  and  lump  coal  were  to  be  made,  one  sample  was  tightly  sealed  in 
an  ordinary  pint  fruit  jar,  while  the  corresponding  sample  was  exposed 
on  an  uncovered  balcony  out  of  doors  for  eleven  months  in  an  un- 
covered tin  can  provided  with  a  diaphragm  or  bottom  of  fine  wire 
gauze. 

Rain  and  snow  fell  upon  the  coal,  but  the  wire  diaphragm  permit- 
ted the  water  to  drain  off,  while  a  paper  disk  placed  upon  the  wire 
gauze  prevented  the  coal  from  sifting  through  the  meshes. 

The  lump  samples  were  exposed  in  pans  of  much  larger  size,  which 
were  provided  with  holes  to.  let  the  water  drain  off. 

At  the  end  of  eleven  months  all  the  samples  were  analyzed  by  Mr. 
Henry  J.  Williams,  together  with  a  sample  of  Pocahontas  coal  that 
had  been  exposed  in  a  coal -yard  for  three  years,  and  one  of  Cumber- 
land coal  that  had  been  under  cover  for  three  years. 

In  these  analyses  the  percentages  of  ash  in  some  of  the  exposed 
samples  are  unfortunately  too  high,  for  a  little  gravel  was  accidentally 
washed  off  the  roof  of  the  house,  by  the  rain,  into  some  of  the  cans. 

higher  value,  7573  calories.     The  Wyoming  coals  have  therefore  a  far  greater 
range  of  variability  than  any  of  the  other  coals  which  have  been  considered  above. 


STEAM-BOILER  ECONOMY. 


This,  however,  in  no  way  affects  the  relative  percentages  of  combust- 
ible matter  free  from  ash. 

The  British  thermal  units  are  calculated  from  the  analyses  by  the 
formula:  1460  +  620(H  -  J0)+  40S. 

The  average  of  the  results  obtained  shows  that  weathering,  under 
the  conditions  described,  decreases  the  percentage  of  carbon,  hydro- 
gen, nitrogen;  increases  the  percentage  of  oxygen,  and  does  not 
materially  alter  the  percentage  of  sulphur. 

ANALYSES   AND   HEATING   VALUES   OP    WEATHERED   AND   UNWEATHERED    COALS. 


Coal,Prox.Anal. 

Ultimate  Analysis  of  Combustible. 

Combustible. 

V 

g 

gs 

£ 

i, 

0) 

£ 

, 

& 

1 

Ill 

*5 

II 

£H; 

3 

§ 

1 

g 

1 

a 

p| 

K.  Q; 

c  *•* 

!rN 

«£ 

1 

4 

I 

1 

R 

I 

1 

.    11 

lew 

B 

03 

S 

0 

H 

o 

a 

h 

K 

J 

B 

1.61 

11.74 

78.94 

5.56 

9.55 

1.52 

4.43 

56.5 

14,406 

Ax 

1.91 

12.61 

79.59 

4.89 

9.75 

1.54 

4.23 

56.9 

14,065 

341 

C 

1.21 

8.69 

83.54 

5.69 

5.87 

1.63 

3.27 

63.6 

15,4(;3j  15,461 

Dx 

1.07 

9.15 

82.55 

5.24 

7.94 

1.64 

2.62 

67.0 

14,792  15,301 

61  It 

P 

1.36 

8.97 

81.24 

5.90 

8.16 

1.79 

2.91 

58.0 

15,003 

Ex 

0.89 

10.02 

81.56 

5.67 

8.14 

1.69 

2.94 

57.8 

14,^08 

95 

R 

1.07 

8.77 

82.47 

6.01 

6.81 

1.88 

2.83 

56.5 

15,353 

Sx 

1.39 

8.50 

82.15 

5.95 

7.10 

1.62 

3.17 

57.5 

15,260 

93 

I 

0.53 

4.34 

88.72 

5.22 

3.79 

1.74 

0.53 

77.2 

15,913 

Hx 

1.12 

6.32 

88.05 

5.04 

4.08 

1.78 

1.04 

75.8 

15,705 



j  ~uo- 

K 

2.02 

10.08 

81.45 

5.62 

10.19 

1.66 

1.09 

61.2 

14,622 

1  gam 

Jx 

1.46 

11.06 

81.33 

5.67 

9.88 

1.67 

1.45 

60  4 

14,685 

•  •  . 

63 

O 

1.77 

8.44 

83.50 

5.67 

7.13 

1.79 

1.90 

58.5 

15,231 

16,246 

NX 

1.71 

10.47 

82.41 

5.74 

8.39 

1.67 

1.79 

61.4 

15,011 

15,2CC 

220^ 

L 

0.95 

5.75 

88.85 

5.19 

3.03 

2.07 

0.87 

78  2 

15,989 

16,048 

MX 

0.70 

7.77 

88.38 

4.77 

4.35 

1.60 

0.89 

80.6 

15,562 

15,958 

427t 

G* 

0.79 

7.51 

88.90 

4.82 

2.87 

2.04 

1.37 

80.0 

15,799 

Pof 

0.94 

7.06 

91.15 

4.75 

2.15 

1.28 

0.68 

80.6 

16,113 

*  Indoors  three  years.  t  Exposed  in  a  coal  yard  three  years. 

t  611,  2tiO,  and  427,  loss  in  calculated  values.     160,  40,  and  90,  corresponding'loss  by  calorime- 
ter tests. 

Reference  letters:  B,  C,  etc.,  unweathered  coals:  Ax,  Dx,  etc.,  weathered  coals; 
B,  A,  C,  D,  Yorkville  lump,  Portland,  Ohio;  P,  E,  Pittsburg,  Pa.,  fine;  R,  S,  do., 
lump;  I,  H,  New  River,  W.  Va.,  fine;  K,  J,  Nickel  Plate,  fine,  McDonald,  Pa.;  O, 
N,  do.,  lump  ;  L,  M,  G,  Georges  Creek,  Cumberland,  Md.,  fine;  Po,  Pocahontas, 
Va.,  fine. 

The  conclusions  to  be  drawn  from  an  examination  of  the  results- 
Bhown  are : 

1st.  That  weathering  decreases  by  about  two  per  cent  the  theoret- 
ical calorific  power,  as  calculated  by  Dulong's  formula. 

2d.  That  weathering  decreases  by  about  one  half  of  one  per  cent 
the  actual  or  true  calorific  power,  as  shown  by  the  three  results  ob- 
tained with  the  bomb. 


'1EST8  OF  THE  HEATING    VALUE  OF  COALS. 


115 


The  results  obtained  by  Messrs.  Hale  and  Williams  are  plotted  on 
the  diagram  given  below,  with  relation  to  the  fixed  carbon  in  the- 
combustible,  together  with  the  curve  obtained  from  Mahler's  tests. 
The  diagram  shows  that  all  the  coals  containing  over  59$  fixed  car- 
bon in  the  combustible  are  within  3$  of  the  corresponding  position  in 


r.u.  CALORIES. 


16020       8900 
15840      8800 
15CCO       8700 
15480       8600 
1530C       8500 
15120       8400 
14940       8300 
14760      8200 
14580      8100 
14400      8000 
14220       7900 
14040       7800 
138CO       7700 

••P| 

L 
•» 

Mf 
Q 

i^ 

•/ 

/L    .J 

^ 

==s 

*Hl 

^ 

-TC 

. 

MX 

X 

^« 

*^^ 

*••»• 

•^> 

-- 

•0 

•  r 

\\ 

> 

^s 

N.x_ 

--- 

—  • 

^ 

Sv 

— 

/ 

X, 

NX 

^S. 

^- 

P. 

— 

L,G,J,C,ETC.UNWEATHERED  COALS. 
Mx,Hx,Ox,ETC.  WEATHERED  COALS. 
THE  POSITIONS  JOINED  DY  DOTTED  LINES 
REPRESENT  RESULTS  OF  CALORIMETRIC 
DETERMINATIONS;  THOSE  JOINED  BY 
FULL  L  NES  SHOW  RESULTS  CALCULATED 
FROM  ANALYSES. 

a* 

/ 

s 

\ 

'EX 

Kr- 

^J 

\ 

B 

\ 

\ 

Ax 

80    79    78     77    7C    75    74    73    TZ    71    70    C9    68    67    CC    65    64    63    62    01    60    59    58    57    5C 

FIG.  10.— HEATING  VALUE  OF  WEATHERED  AND  UNWEATHERED  COALS. 
the  curve,  with  the  exception  of  the  result  calculated  from  the  ulti- 
mate analysis  of  the  weathered  coal  D.  The  exception  is  apparently 
due  to  an  error  in  the  analysis.  The  proximate  analysis  of  this  coal 
shows  an  increase  in  the  fixed  carbon  by  weathering  of  3.68$,  referred 
to  combustible,  while  the  ultimate  analysis  shows  a  decrease  in  the 
total  carbon  of  0.99$.  These  figures  appear  incompatible. 

The  coals  containing  less  than  59$  fixed  carbon  show,  in  most 
cases,  a  wide  divergence  from  the  curve,  tending  to  confirm  the  con- 
clusion drawn  from  the  work  of  Lord  and  Haas,  that  among  the 
highly  volatile  coals  each  class  of  coal  has  a  law  of  its  own. 

Coals  AB  and  CD,  both  said  to  be  Portland  lump,  from  Yorkville, 
Ohio,  show  such  a  great  difference  in  percentage  of  fixed  carbon  and 
in  heating  value  that  they  appear  to  belong  to  entirely  different  classes 
of  coal.  It  would  be  interesting  to  know  whether  these  samples  came 
from  the  same  seam  or  from  different  seams.  If  from  the  same  seam, 
the  figures  would  indicate  that  the  conclusion  of  Professors  Lord  and 
Haas,  that  the  coals  mined  from  one  seam  over  a  considerable  area  of 
country  have  a  nearly  uniform  heating  value,  has  some  exceptions. 

It  should  be  noted  that  the  loss  in  heating  value  per  pound  of  the 
combustible  portion  of  the  coal  may  not  be  a  true  measure  of  the  actual 
loss  in  heating  value  of  the  whole  of  a  given  lot  of  coal,  for  besides 
the  loss  in  heating  value  per  pound  there  may  be  also  a  loss  in  weight, 
and  this,  if  any,  expressed  as  a  percentage,  should  be  added  to  the 


116  STEAM-BOILER  ECONOMY. 

loss  in  heating  value  per  pound.  On  the  other  hand,  there  may  be  a 
gain  in  weight  due  to  oxidation.  In  most  of  these  samples  the  oxygen 
seems  to  have  increased. 

Weathering  of  Coal. — The  practical  effect  of  the  weathering  of 
coal,  while  sometimes  increasing  its  absolute  weight,  is  to  diminish 
the  quantity  of  carbon  and  disposable  hydrogen  and  to  increase  the 
quantity  of  oxygen  and  of  indisposable  hydrogen.  Hence  a  reduc- 
tion in  the  calorific  value. 

An  excess  of  pyrites  in  coal  tends  to  produce  rapid  oxidation  and 
mechanical  disintegration  of  the  mass,  with  development  of  heat, 
loss  of  coking  power,  and  spontaneous  ignition. 

The  only  appreciable  results  of  the  weathering  of  anthracite  within 
the  ordinary  limits  of  exposure  of  stocked  coal  are  confined  to  the 
oxidation  of  its  accessory  pyrites.  In  coking  coals,  however,  weather- 
ing reduces  and  finally  destroys  the  coking  power,  while  the  pyrites  are 
converted  from  the  state  of  bisulphide  into  comparatively  innocuous 
sulphates. 

Eichters  found  that  at  a  temperature  of  158°  to  180°  Fahr.,  three 
coals  lost  in  fourteen  days  an  average  of  3.6$  of  calorific  power. 

It  appears  from  the  experiments  of  Eichters  and  Eeder  that  when 
there  is  no  rise  in  the  temperature  of  coal  piled  in  heaps  and  left  ex- 
posed to  the  air  during  nine  to  twelve  months,  it  undergoes  no  sensible 
change  in  any  respect;  and  that,  on  the  other  hand,  when  the  coal  be- 
comes heated,  it  suffers  precisely  the  same  kind  of  change  that  was 
found  by  Eichters  to  be  effected  in  coal  by  heating  it  in  contact  with 
atmospheric  air  to  a  comparatively  low  temperature,  namely  loss  of 
carbon  and  hydrogen  by  oxidation  and  increase  of  the  absolute  weight 
of  the  coal  owing  to  the  fixation  of  oxygen.* 

Composition  and  Heating  Values  of  German  Coals. — The  table  on 
pages  117  and  119  is  abstracted  from  a  paper  by  H.  Bunte  and  P.  Eitner, 
in  ' '  Zeitschrif t  des  Vereines  Deutscher  Ingenieure,"  May  26,  1900. 
In  the  original  the  heating  values,  as  determined  by  the  Mahler  calo- 
rimeter and  as  calculated  from  the  ultimate  analysis,  are  reduced  by  a 
*' correction"  for  the  latent  heat  of  evaporation  of  water.  The  for- 
mula used  in  the  calculation  from  the  analysis  was  81C+250(H— 10) 
_|_  25S  —  6W,  in  which  C,  H,  0,  S,  and  W  are  respectively  the  percent- 

*  Reports  of  3d  Geological  Survey  of  Pennsylvania,  vol.  M.M.,  p.  113;  also 
Percy's  "Metallurgy:  Refractory  Materials  and  Fuel,"  1873.  See  also  papers 
l>y  R.  P.  Roth  well,  Trans.  A.  I.  M.  E.,  vol.-  iv.  p.  55,  and  by  I.  P.  Kimball, 
Trans.  A  I.  M.  E.,  vol.  viii.  p.  204. 


TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


117 


ANALYSES  AND  HEATING   VALUES   OF   GERMAN   COALS— BUNTE. 


. 

Air-dried  Coal. 

I  Fixed  Carbon  —  rer 
cent  Combustible. 

Combustible. 

Calculated 
Heating  Value 
of 
Combustible. 

?! 

iD  U 

22 

13 

1 
$ 

4 

<3 

C 

H 

D+N 

S 

1 
o 

g 

gf 

«ft 

Ruhr  Coals. 
1    Bickel'eld        .           

81.99 
75.67 
70.04 
56.11 
73.97 

65J2 
83.55 
66.92 
71.14 
63.50 
76.32 
73.96 
72.19 
71.70 
53.96 
71.96 

13.23 
16.64 
23.71 
24.83 
21.04 

28.  m 

14.12 
28.04 
24.98 
24.59 
13.04 
20.19 
22.23 
19.99 
25.67 
17.32 

0.80 
1.09 
1.14 
2.07 
1.84 
2.18 
1  54 
0.70 
1.42 
0  59 
1,51 
0.80 
0.99 
1.49 
1.28 
2.50 
0.57 
1  52 

3.98 
6.60 
5.11 
16.99 
3.15 
2.43 
4.96 
1.63 
3.62 
3.29 
10.40 
9.84 
4.86 
4.09 
7.03 
17.87 
10.15 
2  78 

86.1 
82.0 
74.7 
69.3 
T.S 

69  '.5 
85.5 
70.5 
"4.0 
72,9 
85.'4 
78.6 
76.5 
78.2 
67.8 
80.6 

89.93 
86.23 
87.27 
85.85 
89.65 
83.10 
86.19 
91.40 
86.31 
82.24 
85.43 
89.62 
88.53 
87.52 
89.05 
83.14 
88.82 
84.60 
86.33 
89.55 

4.24 
4.59 
5.17 
5.23 
4.62 
5.38 
5.28 
4.51 
5.07 
5.13 
5.15 
4.12 
5.07 
4.82 
4.90 
5.40 
4.88 
5.28 
5.43 
5  9.] 

3.74 
7.37 
6.53 
7.87 
4.62 
10.86 
7.33 
2.81 
6.97 
10.95 
7.63 
4.59 
5.31 
6.58 
4.38 
9.33 
5.22 
9.70 
6.72 
3.9r 

2.09 
.20 
1.03 
1.05 
1.11 
0.66 
1.20 
1.28 
1.65 
1.68 
1.79 
1.67 
1.07 
1.08 
.67 
2.13 
.08 
0.42 
1.52 
1   W 

8,661 
8,324 
8.64-.' 
8.489 
8,r,30 
8,182 
8,582 
8.914 
8,523 
8,046 
8,455 
8,568 
8.763 
8,539 
8,842 
8,291 
8,723 
8,311 
8,655 
8,957 

15.6'>6 
14.983 
15,556 
15.280' 
15714 
14,728 
15,448 
16,045 
15,:J41 
14.483 
15.219 
15,422 
IS.^S 
15.370 
15.916 
14.924 
15.701 
14,960 
15,579 
16,123 
14.852 
15,673 
1(5.159 
15,521 

15,106 
15,210 
14,864 
15.179 
14,006 
15136 
14,458 
15,152 
14,515 
14,279 
14,414 

13,462 
12,933 

13,247 
11.178 
12,004 

13,2F4 
10,169 
12,184 
13,106 

11,860 

10,463 
9.254 
9,911 

15,860 
15,971 

15.667 
15,932 

2    Bonifacius 

4    Dahlbusch.  .  .  .          

5.  Daniienbaum  
6.  E\vald  
7.  fried  rich  Ernestine  
8.  Frohliche  Morgeusonne  .  . 

10    Graf  BcMist                 .... 

11    Graf  Moltke  

12    Horde 

13.  Holland  
14    Lothringen                 

15.  Mathias  Stinnes  
16.  Mont  Cenis  
17.  Oberhausen  
18   Pluto       

66.90 
71.53 
70.46 
69.  7f> 
72.43 
67.03 

59.72 
54.38 
54.43 
56  13 

27.18 
20  44 
25.28 
21  .52 
18.55 
25.03 

33.19 

37.21 
37.14 
29  17 

1.44 
1.10 
0  98 
0.92 
1.18 
1.64 

1.32 
1.99 
2.03 
2  24 

4.48 
6.93 
3.28 
7.81 
7.84 
6.30 

5.77 
6.4X. 
6.40 
12.46 

71.1 

77.8 

20.  Shamrock   
21    Victoria  Mathias        . 

73.6 
76.4 
79.6 

72.8 

64. 
59. 
59. 
65. 
59. 
68. 
64. 
!59. 

eo! 

63. 

62. 

54. 

48. 

41. 
46. 
42. 

36. 
41. 
i41 
43. 

41. 

33. 
34.4 
35.5 

84.  C 
86.  C 

76.  (1 

Kl> 

84.31 
87.39 
89.43 
86.65 

84.23 

84.51 
83.21 
82.38 
80.95 
85.38 
81.92 
83.32 
81.37 
80.94 
80.79 

73.14 
70.50 

73.08 
68.20 
68.89 

71.70 
65.62 
65.93 

71.57 

65.81 

63.02 
57.11 
60.61 

90.79 
90.94 

88.55 
90.13 

5.01 
5.23 
5.23 
5.16 

5.50 
5.50 
5.45 
5.44 
4.93 
5.23 
5.29 
5.65 
5.57 
5.39 
5.60 

5.57 
5.65 

5.81 
4.86 
5.69 

6.54 
4.92 
5.91 

5.88 

5.81 

5.73 

5.84 
5.72 

4.42 

4.60 

4.87 
4.47 

9.05 
5.96 
3.66 
6.17 

9.22 
8.6r 
10.1 
11.2 
12.8 
8.7 
11.6 
8.7 
12.0 
12.7 
12.5 

15.1 
16.1 

17.3 
25.0 
22.7 

18.5 
26.5 
19.9 
16.8S 

21.82 

30.76 
36.29 
33.26 

3.41 

3.48 

5.28 
3.92 

1.63 
1.42 
1.68 
2.02 

1.05 
1.37 
.21 
0.91 
1  31 
0.68 
1.14 
2.28 
1.03 
0.94 
1.10 

6.14 

3.74 
1.88 
2.66 

3.20 
2.92 
8.20 
5.66 

6.56 

0,49 
0.76 
0.41 

1 

1.38 
0.98 

1  30 

1.48 

8,251 
8,707 
8.977 
8,623 

8.392 

8^50 
8,258 
8,133 
7,781 
8.409 
8,032 
8,418 
8,064 
7,933 
8,008 

7,479 
7,185 

7,304 
6,210 
6,669 

7,380 
5.983 
6,769 
7,281 

6,589 

5,813 
5,141 
5,506 

8.811 
8,873 

8,704 
8.8M 

22    Vollmond               

23    Westende                  .... 

24.  Zollvereia  

Saar  Coals. 
1.  Dudvveiler  

2    Frankenholz 

3.  Fried  richsthal  

4    Heinitz                .... 

50.93 
65.6: 
59.0:, 
54.32 

54.  5b 
53.7:. 
56.08 

43.1 
33.0 

23.2 

24.4 
27.2 

18.8 
27.4 
19.6 
27.6 

18.1 

25.9 
27.6 
22.6 

77.5 
77.50 

69.42 

34.40 
29.81 
32.67 
37.72 
35.74 
31.12 
34.25 

36.13 
34.69 

33.3S 
28.23 
37.28 

33.02 
38.64 

27.57 
35.83 

25.65 

52.28 
52.7? 
41  26 

14.16 
12.63 

21.8? 
13.98 

3.90 
1.73 
3.61 
1.21 
4.  On 
3.93 
3.45 

7.37 
,10.18 

36.26 
45.33 
27.13 

48.68 
:22.85 
47.45 
29.27 

40.35 

16.47 
14.06 
29.14 

1.06 
1.77 

1.7fi 
2.  in 

10.77 
2.83 
4.70 
6.75 
5.6E 
11.23 
i  6.22 

13.31 
22.05 

7.08 
1  1.99 
8.32 

9.49 
11.06 
1  5.35 
7.29 

15.89 

5.28 
5.52 
6.91 

7.26 
8.10 

6  93 

«  15 

6    St  Ingbert  

7.  Itzenplitz  
8.  Konig  
9.  Kohhvald  

10    Piittlingen 

11    Reden          .. 

Upper  Bavaria  Coals. 
1.  Haushamer  Grobkohle.. 
2.  Pensberger  Forderkohle 

Saxon  Brown  Coal. 
1.  Alfred  
2.  Bach  bei  Ziebingen  
3.  Meuselwitz,  Fortschritt  . 
4.  Gnadenhiitte    bei     Miih- 

7.  Marie  Louise  
Lignite  and  Turf. 
1.  Lignit    von    Josefszeche 
in  Schwanenkirchen... 
2.  Pressrorf  von  Hofmark- 

(3)Ostraoh  (turf)  
4.  Turf  of  Pschorrschwaige 
Stone-coal  Briquettes. 
1.  Dahlhausen  Tiefbau  
2    Haniel  &  Co                 

3.  Hugo    Stinnes,      Strass- 
bure:  
4.  Stachelbaus  &  Buchloh  . 

118 


SJEAM  BOILER  ECONOMY. 


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^   FIG.  11.—  GERMAN  C( 
HEATING    VALUES 

^          PER  CENT  OF  FlXK 
g          BON    IN    THE    COM 
O          BLE. 
b 

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without  the  corre 
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>       Lord  and  Haas.    ; 
accompanying  dia 
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plotted    together 
the  curve  deducec 
Mahler's    figures, 
comparison. 

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TE8T8  OF  THE  HEATING    VALUE  OF  COALS. 


119 


ANALYSES  OF  GERMAN  COALS—  Continued. 


Air-dried  Coal. 

1  Fixed  Carbon  —  Per 
cent  Combustible. 

Combustible. 

Calculated 
Heating  Value 
of 
Combustible. 

1  Fixed 
Carbon, 

Volatile 
Matter. 

Water. 

4 

<j 

C 

H 

O+N 

S 

Calories. 

Ejj 

tta 

Silesian  Coals. 
1.  Deutschland  (Gottesberg) 
2.  Viktor    .  

62.29 
74.63 

32.69 
16.89 

1.58 
1.65 
1.67 

2.28 
2.05 
1.95 

8.91 
3.50 
3.68 

15.77 
14.77 

18.95 
19.40 

10.26 
13.65 
16.57 

1.53 
1.79 
1.79 
2.33 
0.96 

3.73 

1.71 

3.44 
6.83 
5.05 
12.48 
4.32 
3.12 

3.52 
5.50 
3.22 

7.73 
5.33 

5.50 
6.68 

18.52 
9.94 
10.49 

10.74 
10.27 
7.42 
11.18 
6.52 

6.41 
6.50 

65.6 

81.5 

Q8.Q 
67.8 
64.3 

64.2 

42.0 
43.6 

44.2 

43.4 
40.4 
40.6 

96.4 
96.8 
99.8 
97.1 
99.2 

97.9 
97.8 

75.70 
88.64 
83.29 
82.83 
83.64 
77.91 

81.59 
82.00 
81.58 

71.05 
70.00 

68.49 
69.98 

67.68 
70.23 
69.88 

93.50 
94.28 
93.82 
93.28 
95.20 

96.09 
92.93 

4.80 
4.63 
5.20 
5.04 
5.02 
4.64 

5.44 
5.46 
5.74 

6.09 
5.09 

5.61 
5.84 

5.90 
5.99 
5.76 

1.22 
1.14 
0.77 
1.04 
0.84 

0.60 
0.88 

18.29 
5.39 
10.80 
10.29 
10.54 
15.97 

11.49 
10.55 
12.00 

19.88 
23.93 

24.58 
22.15 

22.24 
20.40 
20.91 

4.12 
2.96 
4.45 
4.32 
3.08 

2.23 
5.23 

1.21 
1.34 
0.61 

1.84 
0.80 
1.48 

1.48 
1.99 
0.68 

2.98 

0.98 

1.32 
,.03 

4.18 
3.38 
3.45 

1.16 
1.62 
0.96 
1.36 
0.88 

1.08 
0.96 

7,075 
8,622 
8,138 
8,093 
8,119 
7,649 

8,071 
8,017 
8,135 

7,879 
6,428 

6,499 
6,822 

6,701 
7,000 
6,870 

7,894 
7,992 

7,748 
7,812 
7,940 

7,972 
7,679 

12,735 
15,520 
14,648 
14,567 
14,614 
13,768 

14,528 
14,431 
14,643 

14,182 
11,570 

11,699 
12,280 

12,058 
12,600 
12,366 

14,209 
14,386 
13,946 
14,062 
14,292 

14,350 
13,8-22 

3    G'Mdo 

4.  KG*"  gin  Louise  

58.70 
63.50 
61.07 

56.23 

32.14 
34.84 

33.42 

26.54 
30.13 
33.86 

31.34 

44.36 
45.06 

42.13 

5.  Mathilde        

6.  Paulus  

Saxon  Coals. 
1.  Kaisergrube  Gersdorf  bei 
Oelsuitz 

2.  Vereinigt    Feld   Bockwa- 
Hohndorf  
3.  Zwickau  -  Oberhohndorf 
Wilhelmschacht  

Brown  Coal  Briquettes. 
1.  Stempel  Fiirst  Bismarck  . 
2.  Wurfel-Bdkett  C.  Use. 
3.  Wurfel-Brikett   S.    Rech- 
enberg  &  Cie  
•4.  Stempel  Rositz  

5.  Gewerkschaft  Schwarzen- 
feld  

30.88 
30.84 
29.60 

84.56 
85.14 
90.58 
83.98 
91.78 

87.93 
89  "~5 

40.34 
45.57 
43.34 

3.17 
2.80 
0.21 
2.51 
0.74 

1.93 
2.04 

6.  Stempel  Siegfried.  . 

7.  Zeche  Waldau  

Gas  Coke. 
1.  Bonifacius  (Ruhr)  
2.  Camphausen  (Saar).  .  
3.  Consolidation  (Ruhr)  
4.  Ewald  (Ruhr)              .... 

$.  Heinitz  (Saar)  

6.  Konigin      Louise     (Ober- 
schles.)  

7.  Rhein,     Elbe     u.     Alma 
(Ruhr)  .... 

Selection  of  Coal  for  Steam-boilers. — The  selection  of  the  kind  ot 
coal  to  be  used  in  any  given  boiler-plant  depends:  1,  on  the  relative 
cost  per  ton  of  the  different  kinds  delivered  at  the  boiler;  2,  on  their 
relative  total  heating  value  per  pound  or  per  ton;  3,  on  the  relative 
percentage  of  the  heating  value  which  may  be  utilized  in  the  boiler; 
4,  on  the  maximum  capacity,  or  horse-power,  which  may  be  developed 
by  the  boilers  with  different  coals;  5,  on  the  relative  cost  of  handling 
the  different  coals  and  the  ashes  produced  from  them ;  and  6,  on  their 
relative  smokelessness  when  used  in  the  particular  boilers  and  furnaces 
tinder  consideration. 

In  some  locations  only  one  kind  of  coal  is  practically  available,  as 
when  the  boilers  are  located  near  a  coal-mine,  all  other  kinds  being 
lelatively  too  high-priced  on  account  of  the  freight  that  must  be  paid 


120  STEAM-BOILER  ECONOMY. 

on  them.  In  such  cases,  for  the  best  results,  the  furnace  and  the 
draft  must  be  adapted  to  the  coal  at  hand.  If  the  coal  is  of  poor 
quality,  the  grate  surface  must  be  large  relatively  to  the  heating  sur- 
face. If  it  is  anthracite  pea  or  culm,  the  draft  must  be  strong,  and, 
unless  the  grate  surface  is  very  large,  mechanical  draft  may  be  nec- 
essary. If  the  coal  is  bituminous,  the  area  of  the  grate,  in  proportion 
to  the  heating  surface,  will  depend  on  the  quality;  the  poorer  the 
quality  the  larger  the  grate  required.  In  other  locations  many  different 
varieties  of  coal  maybe  available,  and  then  all  of  the  points  above  enu- 
merated may  have  to  be  taken  into  account  in  making  a  selection. 

Usually  the  coal  which  is  sold  at  the  lowest  price  per  ton  is  the 
most  economical  one  for  those  furnaces  and  boilers  that  are  adapted  to 
it.  Its  price  is  apt  to  be  depreciated  below  the  normal  price  due  to  its 
heating  value,  because  its  market  is  limited  by  the  number  of  boilers 
to  which  it  is  adapted,  and  also  by  the  cost  of  freighting  it  to  more 
distant  markets.  Freight  charges  being  the  same  per  ton  on  poor 
as  on  good  coal,  it  does  not  pay  to  haul  poor  coal  long  distances ;  it  is 
better  to  sell  it  at  a  relatively  low  price  in  nearby  markets.  On  the 
other  hand,  good  coals  are  apt  to  be  relatively  overvalued  in  the  market, 
since  they  can  be  used  in  all  kinds  of  furnaces,  are  more  desirable  in 
every  way,  and  they  may  be  transported  long  distances  to  find  the  best 
markets.  On  this  account  a  boiler  and  furnace  should  be  adapted, 
whenever  possible,  to  use  the  poorest  kind  of  coal  in  the  market. 

But  this  is  not  always  possible.  The  boiler  and  chimney  being 
already  in  place  and  the  requirements  of  the  engines  being  such  that 
the  boiler  must  be  driven  to  its  maximum  capacity,  then  a  coal  must 
be  selected  from  which  this  maximum  capacity  may  be  obtained. 

For  maximum  evaporation  per  pound  of  coal,  that  coal  should  be 
selected  in  which  the  product  of  its  total  heating  value  per  pound  by 
the  percentage  of  this  heating  value  which  may  be  utilized  by  the 
boiler,  is  a  maximum.  For  instance,  suppose  an  anthracite  egg-coal 
of  a  heating  value  of  13,000  heat  units  per  pound  and  a  good  bitumi- 
nous coal  of  14,000  heat  units  are  equally  available,  but  the  furnace  is 
such  that  the  boiler  will  give  75  per  cent  efficiency  with  the  anthracite 
and  only  65  per  cent  with  the  bituminous,  then  the  relative  values  of 
the  two  coals  for  that  particular  boiler  are  975  for  the  anthracite  and 
910  for  the  bituminous.  If  a  semi-bituminous  coal  with  a  heating  value 
of  14,500  heat  units  is  also  available,  and  the  boiler-efficiency  with  that 
coal  is  70  per  cent,  then  its  relative  figure  will  be  1015.  If  maximum 
capacity,  rather  than  economy,  is  the  prime  consideration,  then  tha 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  121 

bituminous  coal,  with  the  lowest  relative  economy  of  the  three,  may 
be  selected  if  it  is  found  that  it  is  more  free- burning  than  the  others, 
so  that  a  larger  quantity  of  it  may  be  burned  in  the  furnace  with  the 
draft  that  is  available.  If  economy  of  cost  is  the  chief  consideration, 
the  boiler  having  ample  capacity  with  either  fuel,  then  that  coal  will 
be  selected  which  evaporates  the  most  water  for  the  least  money,  or  in. 
case  of  the  three  coals  considered,  the  one  in  which  its  price  per  ton 
divided  by  its  relative  value  figure,  975,  910,  or  1015,  as  the  case  may 
be,  is  the  least.  If  their  costs  per  ton  are  respectively  $1,95,  $1.82, 
and  $2.03,  then  the  prices  of  the  coals  are  directly  proportioned  to 
their  available  actual  values  for  the  particular  case,  and  as  far  as  cost 
is  concerned  it  is  a  matter  of  indifference  which  is  selected.  The 
selection  may  then  depend  on  the  trifling  difference  between  the  coals 
in  the  relative  cost  of  handling  them,  or  in  handling  the  ash  made 
from  them,  the  bituminous  coal  usually  requiring  the  greater  labor  on 
the  part  of  the  fireman.  If  the  location  is  in  a  city,  where  smoke  is 
objectionable,  the  anthracite  coal  may  be  selected  on  account  of  its 
smokelessness. 


APPENDIX   TO   CHAPTEE  V. 

TESTING  THE  RELATIVE  VALUE   OF  DIFFERENT  COALS.* 

The  writer  recently  had  occasion  to  make  a  test  of  three  different  lots  of 
coal  for  the  purpose  of  determining  their  relative  fuel  value,  to  be  used  as  a 
basis  of  a  very  large  contract.  During  the  tests  some  facts  were  learned 
which  may  prove  of  importance  in  other  similar  tests,  and  which  show  that 
the  apparent  fuel  value  as  determined  by  a  single  series  of  boiler  tests  under- 
uniform  conditions  may  not  be  the  true  relative  value  in  actual  use. 

This  general  fact  was  shown  by  the  writer  in  a  paper  read  at  the  Cleveland 
meeting  of  the  American  Society  of  Mechanical  Engineers  in  1883,  on  the 
"Evaporative  Power  of  Bituminous  Coal,"  in  which  paper  he  criticised  the 
coal  tests  made  for  the  government  under  the  direction  of  Quartermaster- 
General  M.  C.  Meigs,  and  showed  that  the  relative  value  of  many  bituminous 
coals  as  shown  by  these  tests,  in  comparison  with  anthracite,  was  far  below 
their  real  relative  value.  The  statement  was  then  made  that  "  the  relative 
value  of  bituminous  coal  is  a  variable  quantity,  depending  upon  the  condi- 
tions under  which  it  is  burned." 

Thus  one  Pittsburg  bituminous  coal  tested  by  General  Meigs  gave  a  value 
of  96.8,  as  compared  with  100  for  anthracite,  when  tested  in  one  boiler,  and 
the  same  coal  a  value  of  only  76.2  when  tested  in  another  boiler.  Johnson's, 
tests  in  1844  gave  Pittsburg  coal  a  value  of  80,  and  Babcock  &  Wilcox  Com- 
pany's tests  in  1883  gave  it  a  value  of  99.5,  as  compared  with  100  for  anthra- 
cite. 

*  An  article  by  the  author  published  in  Tie  Engineering  and  Mining  Journal,. 
July  19  1890. 


122 


STEAM-BOILER  ECONOMY. 


It  is  quite  common  to  suppose  that  if  two  coals  are  tested  by  burning  them 
under  the  same  steam-boiler,  under  ordinary  average  conditions,  the  area  of 
grate,  extent  of  heating  surface,  height  of  chimney,  etc.,  remaining  the  same, 
and  one  coal  evaporates  say  eight  pounds  of  water,  while  the  other  evaporates 
•only  seven  pounds,  that  the  first  coal  has  a  higher  fuel  value  than  the  second 
in  the  ratio  of  eight  to  seven.  It  may  or  may  not  be  true,  but  if  it  should 
af forwards  be  found  that  by  changing  the  conditions  for  each  coal,  as  by  alter- 
ing the  ratio  of  heating  to  grate  surface,  by  checking  or  increasing  the 
draft,  or  otherwise,  so  that  a  set  of  conditions,  different  for  the  two  coals, 
might  be  found  which  would  give  a  maximum  performance  for  each  coal,  and 
the  evaporation  of  one  coal  increased  from  eight  to  eight  and  one-half  pounds, 
while  that  of  the  second  was  increased  from  seven  to  nine  pounds,  then  the 
verdict  that  the  first  coal  was  the  better  would  be  reversed.  The  new  state- 
ment would  then  be  made  that  the  second  was  the  better  in  the  ratio  of  nine 
to  eight  and  one-half. 

In  the  tests  under  consideration  it  was  found  that  not  only  is  the  fuel  value 
of  a  coal  dependent  on  the  boiler  and  its  proportions,  on  the  draft,  and  on 
the  fireman,  but  that  in  a  test  with  the  same  boiler,  under  the  same  condi- 
tions, and  with  the  same  fireman,  the  figures  obtained  in  a  boiler  test,  and 
even  in  two  tests  of  each  coal,  would  lead  to  erroneous  conclusions  concerning 
the  relative  value  of  the  two  coals,  if  these  figures  were  not  corrected  by  the 
efficiency  of  the  boiler  as  shown  in  the  several  tests. 

The  following  are  the  principal  figures  from  the  record  of  the  tests  of  the 
three  lots  of  coal  referred  to.  The  tests  lasted  from  9£  to  9|  hours  in  each 
case. 


1 

2 

3 

4 

5 

V 

First  series. 

Second  series. 

A. 

B. 

C. 

A. 

C. 

2024 
43.2 
46.9 
680 
15.7 

6455 
3.19 
187.1 

9.495 
9.28 
90.72 

10.466 
100 

Heating  surface  square  feet....           .        

2024 
50.8 
39.8* 
941 
18.5 

8760.5 
4.33 
253.9 

9.311 

8.42 
91.58 

10.167 
97.14 
98.60 
100 

2024 
50.8 
39.8 
792 
15.6 

6865.3 
3.59 
199 

8.665 
14 
86 

10.076 
96.27 
97.72 
93.06 

2024 

50.8 
39.8 
831 
16.4 

7733.3 
3.82 
224.1 

9  30-2 
9.79 
90.21 

10.311 
98.52 
100 
99.90 

2024 
43.2 
46.9 
746 
17.3 

7024.7 
3.47 
203.6 

9.419 

7.78 
92.22 

10.214 
97.59 

"     per  square  foot  of  grate,  pounds  
Equivalent  water  evaporated  from  and  at  212  de- 

Do.  per  square  foot  heating  surface  per  hour  

Water  evaporated  from  and  at  212  degrees  per 

'Combustible  percent                                

Water  evaporated  from  and  at  212  degrees  per 
pound  combustible,  pounds  
Relative  efficiency  of  boiler,  test  No.  5  =  100  
3  =  100  
Apparent  relative  value  of  coal  No.  1  =  100  
4  -  100    .... 

100 
100 
100 

100.81 
98.38 
98.37 

Relative  value  of  coal  corrected  for  boiler  effi- 
ciency A  —  100         ....            

100 
100 

93.90 
93.91 

98.50 
98.50 

Relative  value  of  coal  from  percentage  of  com- 

The  boilers  were  two  ordinary  horizontal  tubular  boilers,  5  feet  diameter 
16  feet  long,  each  with  52  4-inch  tubes.     Each  boiler  had  a  separate  iron 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.          123 

chimney  28  inches  diameter  and  50  feet  high  above  the  grate.  At  10  square 
feet  of  heating  surface  per  horse-power,  the  two  boilers  should  develop  202.4 
horse-power. 

The  three  coals  were  almost  identical  in  appearance,  all  being  very  friable 
and  bright,  semi-bituminous.  A  proximate  analysis  made  subsequent  to  the 
boiler  test  from  samples  selected  during  the  tests  gave  the  following  analysis 
made  on  dry  coal : 

Coal.  A.  B.  C. 

Fixed  carbon 77.17  74.23  74.29 

Volatile  mutter 17.49  16.39  17.97 


Total  combustible  ..............  94.66  90.62  9226 

Ash  .................................     5.34  9.38  7.74 

The  proportions  of  the  boiler,  grate,  and  chimney  being  judged  as  about 
right  for  developing  the  rated  horse-power  with  good  economy,  it  was  deter- 
mined to  make  a  trial  of  the  three  coals  under  the  maximum  draft  which  the 
chimney  would  give,  and  to  preserve  the  conditions  of  the  three  tests  as  uni- 
form as  possible.  The  firing  was  carefully  watched,  to  avoid  the  possibility  of 
air-holes  being  formed  in  the  rear  of  the  grate  or  in  the  corners;  an  even  bed 
of  coals  10  or  12  inches  thick  was  steadily  carried,  and  the  top  of  the  bed  was 
raked  only  very  slightly  and  at  long  intervals  to  check  the  slight  tendency 
which  the  coal  had  to  coking  on  the  surface. 

Coal  A  was  first  tested,  and  proved  to  be  a  remarkably  good  coal,  burning 
very  freely,  and  making  almost  no  clinker,  the  fine  white  ashes,  with  a  por- 
tion of  the  black  friable  coal,  falling  steadily  through  the  grates,  and  the  ash- 
pit remaining  bright  for  several  hours  after  starting.  The  grates  required  a 
slight  cleaning  by  a  slice-bar  only  once  during  the  test. 

The  results  show  an  evaporation  of  9.311  pounds  of  water  from  and  at  212 
degrees  per  pound  of  coal,  and  10.167  pounds  per  pound  of  combustible  —  not 
as  much  by  from  10  to  15  per  cent  as  would  be  expected  under  the  conditions; 
but  the  deficiency  was  explained  by  a  very  high  temperature  of  the  chimney- 
gases,  considerably  over  680  degrees  by  the  mercury  thermometer.  The  pyro- 
meter unfortunately  got  out  of  order  during  the  test,  and  its  figures  were  un- 
reliable. The  rate  of  evaporation  per  square  foot  of  heating  surface,  4.33 
pounds,  would  scarcely  account  for  the  high  temperature,  and  the  cause  was 
afterward  found  to  be  a  faulty  setting  of  the  boiler,  by  which  the  lower  rows 
of  tubes  were  made  partly  ineffective,  the  upper  rows  carrying  off  the  bulk  of 
the  gases  at  a  high  velocity  and  temperature.  This  condition  being  constant 
during  all  the  tests,  however,  it  did  not  interfere  with  the  test  of  the  relative 
value  of  the  coals.  The  capacity,  253.9  horse-power,  was  25  per  cent  above 
the  rated  capacity  of  the  boilers,  estimating  it  at  10  square  feet  per  horse- 
power. 

The  lesson  to  be  drawn  from  this  test,  in  addition  to  that  learned  about 
the  imperfect  setting,  was  that  with  the  same  setting  better  economy  of  coal 
could  be  gained  by  reducing  the  boiler  capacity,  either  by  checking  the  draft 
or  by  reducing  the  area  of  grate  surface. 

The  test  of  coal  B  was  then  proceeded  with,  the  conditions  being  un- 
changed. The  coal  acted  very  differently  from  coal  A.  Clinker  was  soon 
formed,  and  the  grates  required  frequent  slicing  to  allow  enough  air  to  be  ad- 
mitted to  burn  the  coal  at  a  rate  sufficient  to  cause  the  boilers  to  develop  their 
rated  capacity. 

The  results  gave  a  capacity  of  only  199  horse-power,  or  less  than  the  rat- 
ing. The  evaporation  per  pound  of  coal  was  only  8.665  pounds,  or  93.06  per 
cent  of  that  obtained  with  coal  A,  while  the  efficiency  as  shown  by  the  evap- 
oration per  pound  of  combustible  was  also  nearly  1  per  cent  less.  The  high 


/€<  •;«VTHE?'    ^ 
(  UNIVERSITY 

^ 


STEAM-BOILER  ECONOMY. 

temperature  of  the  chimney-gases  continued,  the  thermometer  rising  to  680 
degrees  before  removal  to  prevent  its  breakage,  but  not  so  rapidly  as  in  the 
previous  test.  The  amount  of  ashes  obtained  in  the  boiler  test,  14.0  per  cent, 
as  against  8.42  per  cent  witty  coal  A,  left  no  doubt  as  to  the  inferiority  of  coal 
B.  It  gave  7  per  cent  less  economy  while  reducing  the  boiler  capacity  nearly 
25  per  cent. 

Coal  C  was  then  tested  under  the  same  conditions.  It  burned  so  nearly 
like  coal  A  that  no  difference  could  be  observed  for  two  or  three  hours,  when 
it  was  noticed  that  the  ash-pit  was  becoming  dark,  and  that  evaporation  was 
not  proceeding  quite  so  rapidly  as  at  first.  The  fire  was  becoming  a  little 
sluggish  through  accumulation  of  ashes.  The  bars  required  to  be  sliced  two 
or  three  times  during  the  test.  The  result  showed  nearly  224.1  horse-power, 
12  per  cent  less  than  with  coal  A,  but  the  evaporation  of  water  per  pound  of 
coal  was  almost  exactly  the  same,  9.302  Ibs.  as  compared  with  9.311  IDS.,  and 
the  apparent  relative  value  of  the  coal  was  99.9  per  cent  of  that  of  coal  A. 
The  evaporation  of  water  from  and  at  212  degrees  per  pound  of  combustible, 
however,  was  higher  than  that  with  coal  A,  in  the  ratio  of  10.311  to  10.167 
Ibs.,  or  as  100  to  98.60. 

It  was  quite  evident  that  the  increased  efficiency  of  the  boiler  when  coal  0 
was  tested  was  due  to  the  ashes  of  the  coal  choking  the  passage  of  air  through 
the  fire  just  to  such  an  extent  as  to  cause  the  coal  to  be  burned  more  slowly, 
under  the  given  conditions  of  grate  area,  setting  of  boiler,  and  chimney  draft, 
and  so  slowly  as  to  allow  of  more  of  the  heat  produced  being  absorbed  by  the 
water  in  the  boiler  and  to  allow  less  of  it  to  pass  up  the  chimney. 

It  was  reasonable  to  infer,  therefore,  that  if  coal  A  had  been  burned  more 
slowly,  as  it  might  have  been,  by  a  slight  checking  of  the  chimney  draft  by 
the  damper,  the  boiler  would  have  shown  as  high  an  efficiency  as  it  did  when 
coal  0  was  tested,  and,  per  contra,  that  if  coal  0  had  been  burned  as  rapidly 
as  coal  A,  the  efficiency  of  the  boiler  with  coal  0  would  have  been  as  low  as  it 
was  with  coal  A.  We  may  then  state  the  problem,  if  coal  0  showed,  a  fuel 
value  of  99.9  as  compared  with  coal  A  when  the  boiler  efficiency  was  relatively 
100,  what  would  it  show  if  the  efficiency  was  reduced  to  98.6  ?  and  solve  it  by 
the  proportion : 

Eff'yC.      Eff'yA.       C.          C.  corrected. 
100    :     98.6  ::  99.9     :    98.50. 

The  figure  98.50  may,  therefore,  be  taken  as  the  corrected  relative  value  of 
coal  C  as  compared  with  coal  A. 

The  two  coals  were  tested  again,  as  shown  in  the  table,  tests  4  and  5,  the 
conditions  being  changed  by  reducing  the  grate  surface  from  50.8  square  feet 
to  43.2  square  feet,  and  thereby  increasing  the  ratio  of  heating  to  grate  sur- 
face from  39.8  to  46.9.  In  other  respects  the  conditions  wei:e  preserved  as 
nearly  as  possible  the  same  as  in  the  former  tests.  As  was  expected,  the 
actual  evaporation  from  and  at  212  degrees  was  increased  for  both  coals,  from 
9.311  to  9.419  for  coal  A,  and  from  9.302  to  9.495  for  coal  C.  The  relative 
efficiency  of  the  boiler  was  also  increased  from  10.167  to  10.214  for  coal  A, 
and  from  10.311  to  10.466  for  coal  B.  Comparing  the  evaporation  per  pound 
of  coal  in  tests  4  and  5,  the  apparent  relative  value  of  coal  C  is  100.81  instead 
of  99.9  as  it  appeared  in  the  comparison  of  tests  1  and  3,  thus  reversing  the 
conclusion  which  might  have  been  drawn  from  the  latter  tests,  which  showed 
that  coal  C  was  one-tenth  of  one  per  cent  inferior  to  coal  A,  and  making  it 
appear  that  it  was  eight-tenths  of  one  per  cent  superior. 

The  relative  efficiency  of  the  boiler  in  tests  4  and  5  was  97.59  for  coal  A 
and  100  for  coal  C.  Making  the  correction  as  before  for  relative  efficiencies, 
we  have  the  problem,  if  coal  C  gave  a  relative  value  of  100.81  when  the  boiler 
efficiency  was  100,  what  would  its  value  be  if  the  efficiency  was  97.59?  and 
the  proportion 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  125 


Eff'yC.      EfTyA.  C.  C.  corrected. 

100     :     97.59  ::  100.81     :     98.38, 

>ivhich  figure  agrees  as  closely  as  should  be  expected  with  the  corrected  rela- 
tive value,  98.50,  found  in  tests  1  and  3,  and  the  average  of  these  results,  or 
98.44,  may  be  taken  as  the  true  relative  fuel  value  of  coal  0,  as  compared  with 
100  for  coal  A. 

The  single  test  of  coal  B,  which  showed  a  relative  fuel  value,  as  compared 
with  A,  of  93.06,  gives  a  value,  when  similarly  corrected  for  boiler  efficiency, 
of  93.90. 

The  three  coals,  A,  B,  and  C,  being  of  the  same  general  quality,  as  deter- 
mined by  the  relative  percentage  of  fixed  carbon  and  volatile  matter,  shown 
by  analysis,  differing  only  in  their  percentage  of  ash,  it  would  naturally  be 
expected  that  their  true  relative  fuel  value  in  practice  under  the  best  available 
•conditions  for  each  coal  would  be  in  direct  proportion  to  the  percentage  of 
total  combustible  matter  actually  burned  in  the  boiler  test,  which  is  found  by 
subtracting  the  ash  and  refuse  withdrawn  from  the  fire  during  the  test  from 
100  per  cent.  Making  the  calculation  of  relative  value  on  this  basis  we  find 
a  most  remarkable  coincidence,  as  follows : 

Pnal  n  Coal  C'  Coal  C, 

uoai  B.       test  No  3       tegt  No  g> 

Corrected  value  by  boiler  test,  A  =  100 93.90  98.50  98.38 

Kelative  value,  by  per  cent  combustible,  A  =  100    93.91  98.50  98.37 

It  will  not  be  safe  to  conclude  from  this  coincidence,  however,  that  it  is  a 
general  rule  that  the  fuel  value  of  coal  is  in  proportion  to  percentage  of  com- 
bustible, for  the  quality  of  the  combustible  matter  varies  in  coals  of  different 
general  chemical  constitution,  and  in  coals  containing  a  very  high  percentage 
of  volatile  matter,  as  in  most  bituminous  coals  mined  west  of  Pittsburg,  it  is 
not  possible  in  any  ordinary  boiler-furnace  to  thoroughly  burn  this  volatile 
matter.  It  may,  however,  be  considered  as  a  general  rule  for  coals  of  approx- 
imately the  same  chemical  constitution. 

It  is  moreover  not  safe  to  generalize  that  the  true  relative  fuel  value  of 
two  coals  may  be  always  obtained  by  multiplying  their  apparent  value  as 
found  in  a  boiler  test  by  the  ratio  of  boiler  efficiencies  found  in  the  tests  of 
the  two  coals;  but  the  rule  may  be  stated  as  follows: 

If  in  a  comparative  test  of  two  coals  of  approximately  similar  chemical 
constitution,  the  apparent  relative  fuel  value  as  shown  by  the  boiler  test  differs 
less  than  the  difference  of  boiler  efficiency  in  the  two  tests,  then  the  apparent 
relative  values  should  be  corrected  for  the  difference  in  boiler  efficiency. 

This  rule  will  apply  in  the  case  of  coals  A  and  C,  since  their  apparent  fuel 
value  varied  only  from  —  0.1  to  +  0.8  per  cent,  while  the  boiler  efficiency 
varied  from  1.4  to  2.41  per  cent,  but  it  does  not  apply  to  the  comparison  of 
coals  A  and  B,  in  which  the  apparent  fuel  value  differed  6.94  per  cent,  while 
the  boiler  efficiency  varied  only  0.87  per  cent. 

The  reason  why  the  application  of  the  rule  is  thus  limited  requires  some 
explanation.  In  the  comparison  of  coals  A  and  C,  it  is  evident  that  the  appar- 
ent relative  value  of  A  is  lower  than  it  should  be  (or  C  higher),  because  A  was 
burned  too  fast,  which  caused  the  lower  efficiency  of  the  boiler,  and  also  that 
its  relative  value  could  in  practice  be  made  greater  by  checking  the  draft, 
without  bringing  the  rate  of  evaporation  below  the  normal  capacity  of  the 
boiler.  In  the  case  of  coal  B,  however,  the  efficiency  of  the  boiler  is  not  lower 
because  the  coal  was  burned  too  fast — in  fact  it  was  burned  too  slowly,  as  the 
boiler  did  not  develop  its  rated  capacity.  Slow  burning  should  of  itself  give 
high  efficiency,  and  that  it  did  not  give  higher  efficiency  than  coals  A  and  G, 
but  lower,  is  no  doubt  due  to  the  fact  that  the  greater  amount  of  ash  and 
clinker  it  made  required  the  fires  to  be  cleaned  oftener,  letting  cold  air  pass 


126  STEAM-BOILER  ECONOMY. 

through  the  fire-door  during  the  operation,  and  an  excess  of  air  pass  through 
the  grates  at  the  time  of  every  cleaning.  By  no  change  of  draft  or  of  grate- 
surface  could  the  efficiency  be  raised,  without  still  further  decreasing  the  al- 
ready low  capacity,  hence  the  correction  for  low  efficiency  should  not  be  made 
to  get  the  practical  fuel  value. 

Making  the  correction  for  boiler  efficiency  in  the  case  of  coal  B  does,  in 
fact,  raise  its  apparent  relative  value  from  93.06  to  93.90,  which  is  almost 
identical  with  the  figure  obtained  from  comparison  of  the  percentage  of  com- 
bustible, 93.91,  and  it  shows  that  if  the  efficiency  of  the  boiler  could,  by  any 
means,  have  been  raised  to  the  same  value  as  was  given  in  the  test  No.  1  of 
coal  A,  then  the  relative  value  would  have  been  93.90;  but  as  the  efficiency 
could  not  have  been  so  raised  without  diminishing  the  capacity  of  the  boiler 
below  its  normal  rate,  the  supposition  is  not  of  practical  value,  and  the  cor- 
rection should  not  be  made.  The  fact  is  that  when  the  ash  in  a  coal  is  so 
great  in  amount  as  to  necessitate  frequent  cleaning  of  the  fires,  its  effect  in 
reducing  the  fuel  value  of  the  coal  is  greater  than  that  due  to  its  mere  per- 
centage. It  reduces  the  capacity  of  the  boiler  as  well  as  its  efficiency,  besides 
giving  extra  trouble  in  handling  the  fires  and  getting  rid  of  the  ash  itself. 

The  writer  is  not  aware  that  other  experimenters  on  relative  values  of  fuel 
have  made  use  of  the  corrections  for  boiler  efficiency  described  above,  but  he 
believes  that  the  corrections,  applied  within  the  limits  indicated,  are  of  suffi- 
cient importance  to  receive  attention  in  future  tests  of  this  kind,  even  when 
the  tests  are  made  for  commercial  and  not  for  scientific  purposes. 

COMPARATIVE    CALORIMETRIC    TESTS    OF    COALS.* 

The  writer,  in  his  paper  on  "The  Efficiency  of  a  Steam-boiler,'* 
presented  at  the  St.  Louis  meeting,  May,  1896  (Trans.  A.  S.  M.  E., 
vol.  xvii.  p.  649),  expressed  the  opinion  that  the  variations  in  results 
of  calorimetric  tests  of  coal  "throw  doubt  upon  all  calorimetric  work 
until  a  sufficient  number  of  tests  shall  have  been  made  by  different 
experimenters  and  with  different  calorimeters  upon  similar  samples, 
and  until  tests  so  made  show  a  reasonable  degree  of  uniformity." 
The  results  of  tests  of  two  coals  by  three  different  calorimeters  were 
given  in  the  paper.  Mr.  Barrus  has  since  made  tests  of  the  same 
coals,  using  his  own  calorimeter,  and  they  have  been  analyzed  by  Mr. 
Henry  J.  Williams,  by  Mr.  C.  H.  Benedict,  and  also  by  some  senior 
students  of  an  engineering  college  in  connection  with  their  thesis 
work.  The  results  of  all  the  calorimeter  tests  and  of  the  heating 
value,  calculated  from  the  analyses,  are  given  below.  Coal  No.  1  was 
from  Jackson  Co.,  Ohio,  and  No.  2  from  New  River,  W.  Va. 


Heating  ^ 
Pound 
,  B.T 
(1) 

'alue  per 
Coal, 
.U.  , 
(2) 

15,200 
13,066 
13,527 
14,631 
14,452 
14,016 
15,215 

Heating  Value  per 
Pound  Combustible, 
.  B.T.U.  v 
(1)               (2) 

14,620    16,210 
13,302    13,799 

Ratio 
CO-Ki). 

1.109 
1.037 

Thompson  calorimeter  (Boston)  ..   11,913 
Thompson  calorimeter  (St.  Louis)  11,894 

13,646 
13,208 
12,145 

15,320 
15,197 
14,885 
15,967 

1.1*23 
1.150 
1.226 

Analysis,  Williams's  12,323 

Analysis,  students'  10,786 

Analysis  Benedict's                        •   .... 

*  Appendix  XIV   to  the   Report   of  the 
.A.  S.  M.  E.,  vol.  xxi.  p.  68. 

Committee  on  Boiler  Trials 

,  Trans. 

TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


The  results  of  Mr.  Barrus's  calorimetric  test  and  of  Mr.  Williams's 
analyses  show  a  fairly  satisfactory  agreement,  but  they. are  so  much 
below  the  results  of  the  Carpenter  calorimeter,  and  so  much  above  the 
results  of  the  Thompson  calorimeter,  that  the  true  heating  value  of 
these  coals  is  still  a  matter  of  doubt.  The  results  of  the  analysis  of 
coal  No.  1  by  the  students  is  so  far  below  the  results  of  the  other  tests, 
of  the  same  coal  that  it  is  of  interest  only  in  showing  what  great 
errors  in  analyses  are  possible.  The  ratio  of  the  heating  values  of  the 
combustible  of  coals  Nos.  1  and  2  show  that  the  relative  values  as  well 
as  the  absolute  values  obtained  by  different  calorimeters  are  apt  to 
vary  widely. 

Mr.  Benedict's  analysis  is  given  by  Professor  Carpenter,  as  follows,, 
on  dry  coal:  C,  85.07;  H,  5.01;  N,  0.82;  0,  3.79;  ash,  4.71;  S,  0.30; 
calculated  heat  value,  15,215  B.T.U.  The  samples  furnished  to  all 
the  experimenters  were  identical.  The  coal  was  crushed  in  a  coffee- 
mill,  thoroughly  mixed,  and  several  small  bottles  were  filled  with 
samples  of  the  crushed  coal  at  the  same  time. 

More  recently  the  writer  has  obtained  comparative  figures  by 
three  different  calorimeters  and  by  analysis  of  two  samples  of  Mt» 
Olive  (111.)  coal,  as  follows: 


Heating  Value 
per  Ib. 
Combustible. 
B.  T.  U. 

Ratio 

(2)  -*-  (1) 

Prof.  R.  C.  Carpenter,  Carpenter  calorimeter  

(1) 
13,700 
13,870 
18,687 
14,020 

(2) 

13,800 
13,968 
13,787 
13,955 

1.007 
1.007 
1.007 
0.99ft 

Prof.  N.  "W.  Lord,  Mahler  calorimeter  

Prof.  W.  B.  Potter,  Thompson  calorimeter  
Analysis  by  Ricketts  &  Banks  

13,819 

13,878 

1.004 

All  of  these  results  show  a  remarkably  close  agreement.  The 
greatest  variation,  that  between  the  results  by  the  Thompson  calorim- 
eter and  by  analysis,  is  only  2.4  per  cent.  These  figures  would  indi- 
cate that  the  Thompson  calorimeter  is  fairly  reliable,  but  a  very  differ- 
ent conclusion  must  be  drawn  from  the  results  of  the  tests  by  two 
Thompson  calorimeters  of  the  Jackson  and  the  New  River  coals,  which 
are  far  below  the  results  obtained  by  the  Carpenter  and  the  Barrua 
calorimeters. 

The  conclusion  to  be  drawn  from  the  two  series  of  tests  tabulated 
above  is  that  closely  concordant  results  may  be  obtained  from  different 
calorimeters  when  properly  handled  by  expert  chemists,  and  that  these 
results  will  agree  with  the  results  calculated  from  accurate  analyses; 
but  that  occasionally  very  erroneous  results  may  be  obtained,  and  that 


128  STEAM-BOILER  ECONOMY. 

a  single  calorimetric  test,  unchecked  by  comparison  with  a  test  by  an- 
other calorimeter,  is  to  be  regarded  with  suspicion,  especially  when  the 
test  is  made  with  a  Thompson  calorimeter,  when  the  reported  heating 
value  per  pound  of  combustible  is  low  compared  with  results  of  other 
tests  of  coal  from  the  same  region,  and  when  the  boiler-efficiency  cal- 
culated from  such  calorimetric  test  is  high. 

APPARATUS    FOE    DETERMINING    ON    A    LARGE    SCALE    THE    HEATING 
VALUE    OF    DIFFERENT   COALS. 

The  tests  of  American  coals  by  Professor  Johnson  in  1842,  and  by 
'General  Meigs  in  1882  (Trans.  A.  S.  M.  E.,  vol.  iv.  p.  249),  were 
made  by  evaporating  water  into  steam  in  ordinary  steam-boilers.  A 
steam-boiler  of  ordinary  construction  is  not  a  good  apparatus  for  de- 
termining the  heating  power  of  a  fuel,  for  the  following  reasons : 

1.  We  can  have  no  assurance  that  the  fuel  is  completely  burned. 
In  all  coals  containing  volatile  matter,   the  distilled  gases  may  be 
chilled  by  the  heating-surfaces  of  the  boiler,  and  escape  into  the  chim- 
ney unburned. 

2.  The  heat  generated  by  the  fuel  is  carried  away  in  four  dif- 
ferent portions :   a,  in  the  steam  which  leaves  the  boiler ;  #,  in  the 
<c  entrained  "  water  which  leaves  with  the  steam;  c,  in  the  waste  gases 
in  the  chimney;  d,  by  radiation  from  the  boiler  and  brickwork.     The 
relative  proportion  of  heat  which  disappears  in  each  of  these  four  dif- 
ferent ways  varies  every  instant,  and  the  measurement  of  any  one  of 
the  portions  is  an  exceedingly  difficult  matter  and  liable  to  great 
errors. 

3.  The  boiler  and  furnace  having  a  large  heat-absorbing  capacity 
in  proportion  to  the  quantity  of  fuel  burned  during  a  test,  it  is  diffi- 
cult to  insure  that  the  conditions  at  the  beginning  and  end  of  a  test 
are  the  same;  that  is,  that  in  addition  to  the  four  outlets  for  the  heat 
of  the  fuel  above  mentioned,  a  fifth  part  of  the  heat  has  not  been  ab- 
sorbed by  the  boiler  and  brickwork  in  making  them  hotter  at  the  end 
of  the  test  than  at  the  beginning. 

The  author  described  and  illustrated  in  1886  (Trans.  A.  I.  M.  E., 
vol.  xiv.  p.  727,  a  proposed  apparatus,  in  which  an  attempt  is  made  to 
avoid  to  a  great  extent  these  sources  of  error.  Its  principal  feature  is 
that  it  is  not  a  steam-boiler  at  all,  but  only  a  water-heater. 

It  consists  of  two  sheet-metal  cylinders,  each  12  ft.  long,  the 
upper  one  4  ft.  in  diameter,  and  the  lower  one  3  ft.,  and  connected 
by  a  short  neck  at  one  end  only.  The  upper  cylinder  is  provided  with 


TESTS  OF  THE  HEATING    VALUE  OF  COALS.  129 

a  fire-box  3  ft.  6  in.  in  diameter  and  6  ft.  long,  and  its  rear  end  is 
filled  with  about  100  2-in.  tubes.  The  lower  cylinder  is  completely 
filled  with  2-in.  tubes.  The  fire-box  is  lined  throughout  with  fire- 
brick, and  contains  a  grate-surface  2  ft.  wide  by  2 £  ft.  long.  A  hanging 
bridge-wall  of  fire-brick  is  placed  in  the  upper  part  of  the  fire-box  in 
the  rear  of  the  bridge-wall  proper  for  the  double  purpose  of  presenting 
a  hot  fire-brick  surface  to  the  flame  before  allowing  it  to  touch  the 
heating-surfaces  of  the  tubes  and  tube-sheet,  and  of  changing  its  direc- 
tion so  as  to  cause  the  gases  to  thoroughly  commingle  and  thus  to  in- 
sure complete  combustion.  In  testing  highly  bituminous  coals,  it 
might  be  advisable  to  have  more  than  one  of  these  hanging  walls,  and 
to  give  the  fire-box  a  greater  length,  to  more  certainly  insure  com- 
plete combustion  of  the  gases.  The  gases  of  combustion  pass  through 
the  tubes  of  the  upper  heater,  then  down  through  a  fire-brick  connec- 
tion into  the  tubes  of  the  lower  heater,  after  leaving  which  they  pass 
into  the  chimney.  Air  is  fed  to  the  fire,  under  the  grate-bars,  through 
a  pipe  leading  from  a  fan-blower.  The  air  is  measured  by  recording 
the  revolutions  of  the  blower,  and  the  measurement  is  checked  by  an 
anemometer  in  the  air-pipe.  Its  weight  should  be  calculated  from  the 
barometric  pressure,  and  its  contained  moisture  should  also  be  deter- 
mined. Its  temperature  should  be  taken  before  it  enters  the  ash-pit. 
The  temperature  of  the  escaping  gases  should  be  taken  by  several 
thermometers,  the  bulbs  of  which  reach  to  different  portions  of  the 
chimney-connection.  Cold  water  is  supplied  to  the  bottom  of  the 
lower  heater  at  the  chimney-end,  its  temperature  being  taken, 
before  it  enters,  by  a  thermometer  inserted  in  the  pipe.  The  water 
supply-pipe  may  conveniently  be  attached  to  the  city  main.  The 
water  passes  through  the  two  heaters  in  an  opposite  direction  to  that 
of  the  gases  of  combustion,  and  escapes  at  the  outlet-pipe  at  the  top 
of  the  upper  heater,  by  which  it  is  taken  to  two  measuring-tanks, 
which  are  alternately  filled  and  emptied.  The  temperature  of  the  out- 
flowing water  is  taken  by  a  thermometer  inserted  in  the  outflow-pipe. 
The  rate  of  flow  of  water  through  the  apparatus  is  regulated,  so  that 
the  temperature  of  the  outflowing  water  does  not  exceed  200°  F. 
The  measuring-tanks  have  closed  tops,  which  prevent  evaporation, 
small  outlet-pipes  being  attached  to  the  top  of  each  which  serve  both 
as  indicators  when  the  tanks  are  full,  and  to  allow  air  to  escape  from 
them  when  they  are  being  filled  with  water. 

The  grate-surface  being  only  5  sq.  ft.  and  the  heating  surface 
about  1000  sq.  ft.,  a  ratio  of  200  to  1,  or  more  than  five  times  the 
usual  proportion  in  a  steam-boiler,  and  the  water  being  much  colder 
than  that  in  a  steam-boiler,  the  gases  of  combustion  should  be  cooled 
down  to  near  the  temperature  of  the  air  supplied  to  the  fire — espe- 
cially when,  as  is  usually  the  case,  the  water  supply  is  colder  than  the 
air.  For  extremely  accurate  tests,  the  water  might  be  cooled  before 
entering  by  a  refrigerating  apparatus,  or  by  ice. 

The  whole  apparatus  being  thoroughly  protected,  by  felting,  from 
radiation,  the  heat  generated  by  the  fuel  is  all  measured  in  the  in- 


130  STEAM-BOILER  ECONOMY. 

crease  of  heat  given  to  the  water  which  flows  through  the  apparatus, 
and  in  the  increase  of  temperature  of  the  gases  of  combustion  as  taken 
in  the  chimney,  over  the  temperature  of  the  air  supplied  to  the  fire. 
This  increase,  however,  being  in  any  case  very  slight,  and  the  quan- 
tity of  air  being  known,  the  amount  of  heat  from  the  fuel  which 
escapes  up  the  chimney  can  be  calculated  with  but  small  chances  of 
error. 


CHAPTER  VI. 
FUELS  OTHER  THAN  COAL. 

Coke, — Coke  is  the  solid  material  left  after  evaporating  the  volatile 
ingredients  of  coal,  either  by  means  of  partial  combustion  in  furnaces 
called  coke-ovens,  or  by  distillation  in  the  retorts  of  gas-works.  Being 
a  smokeless  fuel  it  is  available  for  use  in  the  fire-boxes  of  internally 
fired  boilers,  which  are  not  adapted  to  the  smokeless  combustion  of 
soft  coal,  but  its  use  for  this  purpose  is  quite  limited  on  account  of 
its  cost. 

The  proportion  of  coke  yielded  by  a  given  weight  of  coal  is  very 
different  for  different  kinds  of  coal,  ranging  from  35  to  90  per  cent. 

Being  of  a  porous  texture,  it  readily  attracts  and  retains  water 
from  the  atmosphere,  and  sometimes,  if  it  is  kept  without  proper 
shelter,  from  15  to  20  per  cent  of  its  gross  weight  consists  of  moisture. 

ANALYSES   OF   COKE. 
(From  report  of  John  R.  Procter,  Kentucky  Geological  Survey.) 


Where  Made. 

Fixed 
Carbon. 

Ash. 

Sul- 
phur. 

Oonnell^villc   Pa       (Average  of 

3  samples)  

88.96 

9.74 

0  810 

Chattanooga   Tenn 

4        <          

80.51 

16.34 

1.595 

Birmingham    Ala. 

4        '          

87.29 

10.54 

1.195 

Pocaliontns  Va                   '            ' 

3        <          

92  53 

5.74 

0  597 

New  River  W  Va           '            ' 

8        '          .... 

92  38 

7.21 

0.562 

Big  Stone  Gap   Ky            '            ' 

7        <          

93.23 

5.69 

0.749 

Pressed  Fuel,  or  Briquettes. — A  method  of  making  pressed  fuel 
from  anthracite  dust  is  described  by  E.  F.  Loiseau.*  The  dust  is 
mixed  with  ten  per  cent  of  its  bulk  of  dry  pitch,  which  is  prepared  by 
separating  from  tar  at  a  temperature  of  572°  F.  the  volatile  matter  it 
contains.  The  mixture  is  kept  heated  by  steam  to  212°,  at  which 
temperature  the  pitch  acquires  its  cementing  properties,  and  is  passed 
between  two  rollers,  on  the  periphery  of  which  are  milled  out  a  series 


*  Trans.  A.  I.  M.  E.,  vol.  viii.  p.  314. 


131 


132  STEAM-BOILER  ECONOMY. 

of  semi-oval  cavities.  The  lumps  of  the  mixture,  about  the  size  of  art 
egg,  drop  out  under  the  rollers  on  an  endless  belt  which  carries  them 
to  a  screen  in  eight  minutes,  which  time  is  sufficient  to  coo}  the  lumps, 
and  they  are  then  ready  for  delivery. 

The  enterprise  of  making  the  pressed  fuel  above  described  was  not 
commercially  successful,  on  account  of  the  low  price  of  other  coal. 
In  Europe,  however,  "briquettes"  are  regularly  made  of  coal-dust 
(bituminous  and  semi-bituminous). 

Coal-dust. — Dust  when  mixed  in  air  burns  with  such  extreme 
rapidity  as  in  some  cases  to  cause  explosions.  Explosions  of  flour- 
mills  have  been  attributed  to  ignition  of  the  dust  in  confined  passages. 
Experiments  made  in  Germany  in  1893  show  that  pulverized  fuel 
may  be  burned  without  smoke,  and  with  high  economy.  The  fuelr 
instead  of  being  introduced  into  the  fire-box  in  the  ordinary  manner, 
is  first  reduced  to  a  powder  by  pulverizers  of  any  construction.  In 
the  place  of  the  ordinary  boiler  fire-box  there  is  a  combustion-chamber 
in  the  form  of  a  closed  furnace  lined  with  fire-brick  and  provided  with 
an  air-injector  similar  in  construction  to  those  used  in  oil-burning 
furnaces.  The  nozzle  throws  a  constant  stream  of  the  fuel  into  the 
chamber.  This  nozzle  is  so  located  that  it  scatters  the  powder  through- 
out the  whole  space  of  the  fire-box.  When  this  powder  is  once- 
ignited,  which  is  readily  done  by  first  raising  the  lining  to  a  high 
temperature  by  an  open  fire,  the  combustion  continues  in  a  regular 
manner  under  the  action  of  the  current  of  air  which  carries  it  in. 

Powdered  fuel  was  used  in  the  Crompton  rotary  puddling-furnace 
at  Woolwich  Arsenal,  England,  in  1873.*  It  has  recently  been  adopted 
successfully  in  this  country  in  the  rotary  kilns  used  in  the  manufac- 
ture of  Portland  cement. 

The  American  Manufacturer  of  Dec.  13,  1900,  illustrates  the 
Cyclone  Pulverizer,  a  British  invention,  which  is  said  to  be  in  success- 
ful use  grinding  coal  for  dust-firing.  We  quote  from  it  the  following 
statement  of  the  requisite  conditions  of  success  in  the  use  of  powdered 
fuel,  and  of  the  advantages  claimed  for  it: 

The  best  results  can  only  be  obtained  when  the  following  essentials 
are  complied  with,  viz. : 

(a)  The  fuel   must   be  reduced  cheaply  to  a  very  finely  divided 
powder,  and  must  be  of  a  strictly  uniform  grade. 

(b)  The   coal-powder  mixed  with  air  must  be  carried  in  an  un- 
broken stream  into  .the  combustion-chamber. 

*  Journal  of  the  Iron  and  Steel  Institute,  i.,  1873,  p.  91. 


FUELS  OTHER  THAN  COAL.  133 

(c)  The  air-current  must  be  so  regulated  that  it  will  hold  the  coal- 
powder  in  suspension,  when  within  the  furnace,  until  complete  com- 
bustion is  effected. 

(d)  A  sufficiently  high  temperature  must  be  continuously  main- 
tained in  the  furnace,  to  ensure  perfect  combustion  of  the  powder. 

The  problem  of  how  to  reduce  the  coal  economically  to  the  required 
standards  of  fineness  and  uniformity  is  the  one  tiling  which  has  given 
great  trouble  in  developing  new  devices  in  firing-apparatus. 

The  advantages  of  the  use  of  powdered  fuel  may  be  summarized  as 
follows:  1.  The  most  economical  and  complete  combustion  of  the  fuel, 
in  a  manner  similar  to  gas-firing,  but  without  the  disadvantages  of  that 
.system.  2.  Complete  smokelessness.  3.  Reduced  labor  expenses,  since 
one  man  can  easily  manage  several  furnaces.  4.  Adaptability  and  ease 
of  regulation  to  meet  any  requirements,  especially  when  the  work  is 
that  of  steam-generation.  5.  Decreased  wear  and  tear  of  furnaces,  in 
the  case  of  internally  fired  boilers.  6.  Saving  of  time  in  starting  up 
furnaces,  and  rapid  stoppage  of  firing,  in  case  of  necessity.  7.  Less 
labor  in  removing  refuse,  which  is  light  in  quantity,  and  in  the  form 
of  slag.  8.  Intimate  contact  of  the  fuel  with  the  air,  whereby  the 
minimum  excess  over  the  theoretical  volume  is  employed,  and  waste  of 
heat  thus  avoided. 

Peat  or  Turf,  as  usually  dried  in  the  air,  contains  from  25$  to  30$ 
of  water,  which  must  be  allowed  for  in  estimating  its  heat  of  combus- 
tion. This  water  having  been  evaporated,  the  analysis  of  M.  Reg- 
nault  gives,  in  100  parts  of  perfectly  dry  peat  of  the  best  quality: 
€  58$,  H  6$,  0  31$,  Ash  5$. 

In  some  examples  of  peat  the  quantity  of  ash  is  greater,  amount- 
ing to  7$  and  sometimes  to  11$.  The  specific  gravity  of  peat  in  its 
ordinary  state  is  about  0.4  or  0.5.  It  can  be  compressed  by  ma- 
chinery to  a  much  greater  density.  (Rankine.) 

Clark  ("Steam-engine,"  vol.  i.  p.  61)  gives  as  the  average  compo- 
sition of  dried  Irish  peat:  C  59$,  H  6$,  0  30$,  1ST  1.25$,  Ash  4$. 

Applying  Dulong's  formula  to  this  analysis,  we  obtain  for  the 
total  heating  value  of  perfectly  dry  peat  10,009  heat-units  per  pound, 
.and  for  air-dried  peat  containing  25$  of  moisture  7507  heat-units  per 
pound.  To  determine  the  " available"  heating  value,  we  must  sub- 
tract the  heat  lost  in  the  superheated  steam  in  the  chimney-gases,  as 
Calculated  by  the  formula  on  page  25.  For  each  pound  of  the  air- 
dried  peat  the  superheated  steam  is  0.25  -f-  0.75  X  .06  X  9  =  0.655  Ib. ; 
and  if  the  temperature  of  the  chimney-gases  is  462°  and  that  of  the 
air-supply  62°  the  heat  lost  is 

0.655  X  [(2  -f  2  -  62)  +  966  -f  (0.48  X  250)]  =  810  B.T.U. 


134 


STEAM-BOILER  ECONOMY. 


This  subtracted  from  7507  gives  6697  B.T.TJ.  as  the  available  heating- 
value  per  pound  of  peat. 

Deposits  of  peat  are  found  in  many  places  throughout  the  United 
States  and  Canada,  but  it  has  hitherto  not  been  found  practicable, 
commercially,  to  utilize  them  for  fuel  in  competition  with  coal.  In 
some  countries  in  Europe,  such  as  in  Holland  and  Denmark,  the  peat 
industry  is  quite  common.  Papers  on  peat  and  its  utilization  will  be 
found  in  "  Mineral  Industry,"  vol.  ii.,  1893,  and  vol.  vii.,  1898.  The 
following  table  is  given  showing  the  comparative  and  calorimetric 
value,  analyses  of  wood,  peat,  and  coal,  from  a  report  made  in  Sweden 
in  1896.  The  analyses  are  of  the  fuel  dry  and  free  from  ash. 


Composition. 
Carbon     .  .     . 

Wood. 
52  0 

Peat. 
58  0 

Brown 
Coal. 

660 

Swedish 
Coal. 

78  0 

English 
Steam  Coal. 

81  0 

Welsh 
Anthracite. 

91  0 

Hydrogen  .       • 

6  2 

5  7 

4  6 

5  1 

5  2 

3  5 

41.7 

35.0 

28.0 

14.8 

11  5 

3  5 

{Sulpliur     

08 

1  0 

1  0 

0.1 

1.2 

1.0 

1.3 

1.3 

1.0 

Calories 

4900 

5700 

6000 

7500 

8000 

8600 

B.T.U  

8920 

10260 

10800 

13500 

14400 

15480 

Moisture 20  22  25  13.5  7.6  2.0 

Wood. — Wood,  when  newly  felled,  contains  a  proportion  of  moist- 
ure which  varies  greatly  in  different  kinds  and  in  different  specimens, 
ranging  between  30$  and  $oO,  and  being  on  an  average  about  40$. 
After  8  or  12  months'  ordinary  drying  in  the  air  the  proportion  of 
moisture  is  from  20$  to  25$.  This  degree  of  dryness,  or  almost  per- 
fect dryness  if  required,  can  be  produced  by  a  few  days'  drying  in  an 
oven  supplied  with  air  at  about  240°  F. 

Perfectly  dry  wood  contains  about  50$  of  carbon,  the  remainder 
consisting  almost  entirely  of  oxygen  and  hydrogen  in  nearly  the  pro- 
portions which  form  water,  the  hydrogen  being  somewhat  in  excess. 
The  coniferous  family  contain  a  small  quantity  of  turpentine,  which 
is  a  hydrocarbon. 

ANALYSES  OF  WOODS,  BY  M.  EUGENE  CHEVANDIER. 


Composition. 


Woods. 

Carbon. 

Hydrogen. 

Ox  y  gen. 

Nitrogen. 

Ash. 

Beech 

49  36$ 

601$ 

42  69$ 

0  91$ 

1  06$ 

Oak  

49  64 

5.  92 

41  16 

1  29 

1  97 

Birch  

50  20 

620 

41.62 

1.15 

0  81 

Poplar  

49  37 

6.21 

41.60 

0.96 

1.86 

Willow 

49  96 

5  96 

39  56 

096 

3  37 

Average  .  .  . 

49.70$ 

6.06$ 

41.30$ 

1.05$ 

1.80$ 

FUELS  OTHER  THAN  COAL.  135 

Heating  Value  of  Wood. — According  to  a  table  by  S.  P.  Sharpless,* 
the  ash  varies  from  0.03$  to  1.20$  in  American  woods,  and  the  fuel 
value  ranges  from  3667  (for  white  oak)  to  5546  calories  (for  long-leaf 
pine)  =  6600  to  9883  British  thermal  units  for  dry  wood. 

The  following  table  is  given  in  several  books  of  reference,  the 
authority  and  quality  of  coal  referred  to  not  being  stated. 

The  weight  of  one  cord  of  different  woods  (thoroughly  air-dried)  is 
about  as  follows: 

Hickory  or  bard  maple 4500  Ibs.  equal  to  1800  Ibs.  coal.  (Others  give  2000.) 

Whiteoak 3850    "  "     1540    "      "  (  "         1715.) 

Beech,  red  and  black  oak. ..  3250    "  "     1300    "      "  (  "         1450.) 

Poplar,  chestnut,  and  elm..  2350    "  "       940    "      "  (  "          1050.) 

The  average  pine 2000    "  "       800    "      "  (  "  925.) 

Referring  to  the  figures  in  the  last  column,  it  is  said: 

From  the  above  it  is  safe  to  assume  that  2J  Ibs.  of  dry  wood  are 
equal  to  1  Ib.  average  quality  of  soft  coal  and  that  the  full  value  of 
the  same  weight  of  different  woods  is  very  nearly  the  same — that  is,  a 
pound  of  hickory  is  worth  no  more  for  fuel  than  a  pound  of  pine, 
assuming  both  to  be  dry.  It  is  important  that  the  wood  be  dry,  as 
each  10$  of  water  or  moisture  in  wood  will  detract  about  12$  from  its 
value  as  fuel. 

Taking  an  average  wood  of  the  analysis,  perfectly  dry,  0,  50; 
H,  6;  0,  42;  N  and  ash,  2,  its  total  heating  value,  by  Dulong's 
formula,  is  7765  B.T.U.  per  pound.  If  the  wood  contains  25$  of 
moisture  the  analysis  of  the  moist  wood  is  C,  37.5;  H,  4.5;  0,  31.5; 
N  and  ash,  1.5,  and  its  total  heating  value  is  75$  of  7765,  or  5824 
B.T.U.  per  pound.  To  obtain  the  "available"  heating  value  we 
subtract  the  loss  of  heat  in  the  steam  formed  from  the  water  and  the 
hydrogen  in  the  wood,  as  calculated  by  the  formula  on  page  25. 
Taking  the  temperature  of  the  air  supply  at  62°  and  that  of  the 
escaping  chimney-gases  at  462°,  this  loss  is  810  B.T.U.,  which  sub- 
tracted from  5824  gives  5014  B.T.U.  per  pound  as  the  available  heat- 
ing value. 

Sawdust. — The  heating  power  of  sawdust  is  naturally  the  same  per 
pound  as  that  of  the  wood  from  which  it  is  derived,  but  if  allowed  to 
get  wet  it  is  more  like  spent  tan  (which  see  below).  The  conditions 
necessary  for  burning  sawdust  are  that  plenty  of  room  should  be  given 
it  in  the  furnace,  and  sufficient  air  supplied  on  the  surface  of  the 
mass.  The  same  applies  to  shavings,  refuse  lumber,  etc.  Sawdust  is 

*  Journal  of  the  Charcoal  Iron  Workers'  Association,  vol.  iv.  p.  36. 


136  STEAM-BOILER  ECONOMY. 

frequently  burned  in  sawmills,  etc.,  by  being  blown  into  the  furnace 
by  a  fan-blast. 

Wet  Tan-bark.  —Tan,  or  oak-bark,  after  having  been  used  in  the 
processes  of  tanning,  is  burned  as  fuel.  The  spent  tan  consists  of 
the  fibrous  portion  of  the  bark.  According  to  M.  Peclet,  five  parts  of 
oak-bark  produce  four  parts  of  dry  tan;  and  the  heating  power  of 
perfectly  dry  tan,  containing  15$  of  ash,  is  6100  British  thermal 
units;  whilst  that  of  tan  in  an  ordinary  state  of  dryness,  containing 
30 !$  of  water,  is  only  4284  B.T.TJ.  The  weight  of  water  evaporated 
from  and  at  212°  by  one  pound  of  tan,  equivalent  to  these  heating 
powers,  is,  for  perfectly  dry  tan,  5.46  Ibs.,  for  tan  with  30$  moisture, 
3.84  Ibs.  Experiments  by  Prof.  R.  H.  Thurston  *  gave  with  the 
Crockett  furnace,  the  wet  tan  containing  59$  of  water,  an  evaporation 
from  and  at  212°  F.  of  4.24  Ibs.  of  water  per  pound  of  the  wet  tan, 
and  with  the  Thompson  furnace  an  evaporation  of  3.19  Ibs.  per  pound 
of  wet  tan  containing  55$  of  water.  The  Thompson  furnace  con- 
sisted of  six  fire-brick  ovens,  each  9  feet  X  4  feet  4  inches,  containing 
234  square  feet  of  grate  in  all,  for  three  boilers  with  a  total  heating 
surface  of  2000  square  feet,  a  ratio  of  heating  to  grate  surface  of  9  to 
1.  The  tan  was  fed  through  holes  in  the  top.  The  Crockett  furnace 
was  an  ordinary  fire-brick  furnace,  6x4  feet,  built  in  front  of  the 
boiler,  instead  of  under  it,  the  ratio  of  heating  surface  to  grate  being 
14.6  to  1.  According  to  Prof.  Thurston  the  conditions  of  success  in 
burning  wet  fuel  are  the  surrounding  of  the  mass  so  completely  with 
heated  surfaces  and  with  burning  fuel  that  it  may  be  rapidly  dried, 
and  then  so  arranging  the  apparatus  that  thorough  combustion  may 
be  secured,  and  that  the  rapidity  of  combustion  be  precisely  equal  to 
and  never  exceed  the  rapidity  of  desiccation.  Where  this  rapidity  of 
combustion  is  exceeded  the  dry  portion  is  consumed  completely,  leaving 
an  uncovered  mass  of  fuel  which  refuses  to  take  fire. 

Straw  as  Fuel. — Experiments  in  Russia  showed  that  winter- wheat 
straw,  dried  at  230°  F.,  had  the  following  composition:  C,  46.1;  H, 
5.6;  N,  0.42;  0,  43.7;  Ash,  4.1.  Heating  value  in  British  thermal 
units:  dry  straw,  6290;  with  10$  water,  5448.  With  straws  of  other 
grains  the  heating  value  of  dry  straw  ranged  from  5590  for  buckwheat 
to  6750  for  flax,  f 

Clark  ("Steam-engine,"  vol.  i.  p.  62)  gives  the  mean  composition 
Oi  wheat  and  barley  straw  as  C,  36;  H,  5;  0,  38;  N,  0.50;  Ash, 

*  Journal  of  the  Franklin  Institute,  1874. 
f  Eng'g  Mechanics,  Feb.,  1893,  p.  55. 


FUELS  OTHER  THAN  GOAL.  137 

4.75;  water,  15.75,  the  two  straws  varying  less  than  1$.  The  total 
heating  value  of  straw  of  this  composition,  according  to  Dulong's  for- 
mula, is  5411  heat-units.  Clark  erroneously  gives  it  as  8144  heat- 
units.  Taking  the  temperature  of  the  chimney-gases  at  462°  and 
that  of  the  air-supply  at  62°  the  *'  available  "  heating  value  is 
4660  B.T.U. 

Bagasse  as  Fuel  in  Sugar  Manufacture. — Bagasse  is  the  name 
given  to  refuse  sugar-cane,  after  the  juice  has  been  extracted.  Prof. 
L.  A.  Becuel,  in  a  paper  read  before  the  Louisiana  Sugar  Chemists' 
Association,  in  1892,  says:  "With  tropical  cane  containing  12.5$ 
woody  fibre,  a  juice  containing  16.13$  solids,  and  83.87$  water,  bag- 
asse of,  say,  66$  and  72$  mill  extraction  would  have  the  following 
percentage  composition: 

Woody  Combustible  ,,r  , 

Fibre.  Salts.  Water" 

66#  bagasse 37  10  53 

72$  bagasse 45  9  46 

"  Assuming  that  the  woody  fibre  contains  51$  carbon,  the  sugar 
and  other  combustible  matters  an  average  of  42.1$,  and  that  12,906 
units  of  heat  are  generated  for  every  pound  of  carbon  conaumed,  the 
€6$  bagasse  is  capable  of  generating  2978  heat-units  per  pound  as 
against  3452,  or  a  difference  of  474  units  in  favor  of  the  72$  bagasse. 

"  Assuming  the  temperature  of  the  waste  gases  to  be  450°  P.,  that 
of  the  surrounding  atmosphere  and  water  in  the  bagasse  at  86°  F.,  and 
the  quantity  of  air  necessary  for  the  combustion  of  one  pound  of 
carbon  at  24  Ibs.,  the  lost  heat  will  be  as  follows:  In  the  waste  gases, 
heating  air  from  86°  to  450°  F.,  and  in  vaporizing  the  moisture,  etc., 
the  66$  bagasse  will  require  1125,  and  the  72$  bagasse  1161  heat-units. 

"  Subtracting  these  quantities  from  the  above,  we  find  that  the 
66$  bagasse  will  produce  1853  available  heat-units,  or  nearly  38$  less 
than  the  72$  bagasse,  which  gives  2990  units. 

"  It  appears  that  with  the  best  boiler  plants,  those  taking  up  all 
the  available  heat  generated,  by  using  this  heat  economically  the 
bagasse  can  be  made  to  supply  all  the  fuel  required  by  our  sugar- 
houses." 

Petroleum. — Thos.  Urquhart  of  Russia  gives  the  following  table 
of  the  theoretical  evaporative  power  of  petroleum  in  comparison  with 
that  of  coal,  as  determined  by  Messrs.  Favre  and  Silbermann :  * 

*  Proc.  Inst.  M.  E.,  Jan.,  1889. 


138 


STEAM-BOILER  ECONOMY. 


Specific 
Gravity 

Chem.  Comp. 

Heating 
power, 

Theoret. 
Evap.,  Ibs. 
Watt-  r  per 

Fuel. 

at  3^°  F., 
Water 
=  1.000. 

C. 

H. 

o. 

Thermal 
Units 

Ib.  Fuel, 
from  and 
at  212°  F. 

Penna.  heavy  crude  oil  

S.  G. 

0.886 

p.  c. 
84.9 

13.C7 

Pll 

Units. 
20,736 

Ibs. 
21.48 

Caucasian  light  crude  oil  .  . 
"          heavy     "      ".«.«. 

0.884 
0.938 

86.3 
86.6 

13.6 
12.3 

0.1 
1.1 

22,027 
20,138 

22.70 
20.85 

Petroleum  refuse     

0  928 

87.1 

11.7 

1.2 

19,832 

20.53 

Good  English  coal,  mean  of 
98  samples  

1.380 

80.0 

5.0 

8.0 

14,112 

14.61 

In  experiments  on  Russian  railways  with  petroleum  as  fuel,  Mr. 
Urquhart  obtained  an  actual  efficiency  equal  to  82$  of  the  theoretical 
heating  value.  The  petroleum  is  fed  to  the  furnace  by  means  of  a 
spray-injector  driven  by  steam.  An  induced  current  of  air  is  car- 
ried in  around  the  injector-nozzle,  and  additional  air  is  supplied  at 
the  bottom  of  the  furnace. 

The  following  notes  are  condensed  from  a  paper  on  "  Crude  Petro- 
leum and  its  Products  as  Fuel,"  by  E.  H.  Tweddle.* 

Crude  petroleum  is  a  hydrocarbon,  often  containing  a  small  per- 
centage of  sulphur  and  oxygen  as  impurities.  Its  specific  gravity  may 
vary  from  12°  to  70°  Baume,  but  the  greatest  quantity  produced  ranges 
from  30°  to  45°  Baume.  The  color  of  crude  petroleum  is  usually  a 
green  brown,  but  it  is  found  from  a  light  brown  color,  through  the 
various  shades  of  green  to  a  jet  black.  It  may  be  broken  up  by  distil- 
lation into  benzene,  kerosene,  and  other  distillates  and  residuums  of 
various  qualities,  any  one  of  which  makes  a  very  good  fuel  under 
certain  conditions. 

Gasoline,  or  petroleum  distillate  of  more  than  74°  Baume,  will 
never  be  used  for  fuel  except  to  a  very  limited  extent,  since  it  and 
its  closely  associated  distillates  are  always  more  valuable  for  other 
purposes. 

Benzene,  or  petroleum  distillate  from  55°  to  74°  Baume,  is  the 
best  of  all  liquid  fuels,  but  its  use  is  restricted  owing  to  the  care  with 
which  it  has  to  be  handled.  The  difficulty,  danger  and  expense  of 
transporting  will  only  allow  of  its  use  in  a  very  few  favored  localities. 

Kerosene  or  petroleum  distillate  of  from  48°  B.  to  35°  B.  gravity 
is  an  excellent  fuel,  but,  owing  to  the  expense  attending  its  prepar- 
ation, we  can  hardly  expect  to  see  the  price  fall  below  3c.  per  gallon, 
except  in  the  places  where  it  is  produced;  for,  should  it  generally  be- 


*  Engineering  and  Mining  Journal,  Oct.  14,  21,  and  28,  1899. 


FUELS  OTHER  THAN  COAL.  130 

come  so  cheap  the  consumption  of  it  as  an  illuminant  would  increase 
so  enormously  that  there  would  be  little  left  for  fuel. 

The  present  price  of  kerosene  in  bulk  and  in  large  quantity  may 
be  taken  at  about  3c.  per  gallon  at  its  place  of  production,  both  in 
Russia  and  America.  As  a  fuel  for  small  boilers,  it  is  the  best, 
because  of  its  portability  and  the  safety  and  facility  with  which  it 
can  be  handled. 

Next  to  kerosene,  some  of  the  heavy  distillates  of  petroleum  known 
as  neutral  or  solar  oils  could  be  used  as  fuel,  but  they  have  no  par- 
ticular advantage  over  kerosene,  save  their  high  fire-test. 

Crude  petroleum  may  contain  any  portion  of  benzene  and  kerosene 
from  nothing  up  to  nearly  90  per  cent,  varying  entirely  with  the  lo- 
cality where  it  is  produced.  We  may  say  roughly  that  of  these  two 
distillates,  American  crude  petroleum  contains  50  to  75  per  cent  of 
kerosene  and  benzene;  Russian  from  15  to  50  per  cent;  Peruvian 
from  15  to  50  per  cent. 

If  distillation  is  stopped  after  the  benzenes  and  kerosenes  have  been 
run  off,  there  remains  in  the  still  an  oil  known  by  the  various  names 
of  residuum,  reduced  oil,  tar,  fuel-oil,  astatki,  mazoot,  petroleum 
refuse,  etc. 

If  the  distillation  of  this  residuum  is  pushed  still  farther,  neutral 
and  lubricating  oils  distill  over,  or  else,  with  certain  forms  of  stills, 
decomposition  sets  in,  and  various  products  may  be  distilled  over, 
until  nothing  but  a  small  amount  of  coke  is  left  in  the  still. 

The  demand  for  mineral  lubricating  oils  is  so  great  in  the  United 
States  that  but  little  residuum  would  be  placed  on  the  market  at  a 
price  which  would  render  it  available  as  a  fuel-oil.  In  Russia,  how- 
ever, where  the  crude  oil  contains  a  low  percentage  of  kerosene,  there 
is  an  enormous  surplus  of  residuum,  which  cannot  all  be  used  for  the 
manufacture  of  lubricating  oils.  It  is  generally  known  as  "astatki" 
or  "mazoot, "and  is  used  for  fuel  in  all  possible  places.  This  as- 
tatki is  the  fuel-oil  par  excellence  for  marine  and  locomotive  work 
where  a  perfectly  safe  oil  is  required.  It  is  now  distributed  largely 
over  the  Russian  Empire,  and  in  1890  some  600,000  tons  were  used 
for  interior  navigation  in  Russia  alone,  and  the  consumption  has 
been  constantly  increasing. 

The  eastern  petroleum  region  of  the  United  States  is  about  400 
miles  from  the  seaboard,  and  although  many  pipe-lines  traverse  this 
distance,  there  must  be  an  expense  connected  with  the  carriage  of  the 
crude  oil.  The  petroleum  fuel  consumed  in  the  United  States  is 


140  STEAM-BOILER  ECONOMY. 

almost  restricted  to  the  use  of  crude  oil,  and  this  is  not  the  fuel  which 
will  suit  the  general  consumer,  especially  if  he  is  to  use  the  oil  for 
either  railroad  or  marine  purposes.  Crude  oil  is  a  most  excellent  and 
easily  handled  fuel,  but  it  must  be  used  with  caution,  and  is  abso- 
lutely unfit  for  use  on  alocomotive  or  steamer,  since,  in  case  of  accident, 
it  may  catch  fire  and  spread  with  startling  rapidity.  For  such 
purposes  no  petroleum  should  be  used  that  has  a  fire-test  of  less  than 
200°  to  250°  Fahrenheit.  A  petroleum  oil  with  a  fire-test  of  250°  F. 
is  a  safer  fuel  than  coal. 

Eesiduum  oil  which  has  a  fire-test  of  say  250°  to  300°  F.  is  the 
most  suitable  for  fuel  on  steamers,  since  it  is  absolutely  safe,  as  it  can- 
not take  fire  and  does  not  give  off  inflammable  gases  until  heated  to  a 
temperature  above  that  of  boiling  water.  As  the  fuel  would  be  carried 
in  tanks  below  the  water-line,  heating  to  that  degree  becomes  a  prac- 
tical impossibility.  Such  oil  may  be  placed  in  a  bucket  and  stirred 
with  a  red-hot  poker  without  catching  fire;  shovelsful  of  hot  coals 
may  be  thrown  into  it,  but  they  will  sink  and  be  extinguished  the 
same  as  if  thrown  in  water. 

It  is  probable  that  in  the  future  petroleum  fuel  will  be  used  more 
for  marine  purposes  on  account  of  economy  in  space  and  weight.  Cal- 
ifornia petroleum  will  probably  be  largely  used  for  this  purpose,  as  the 
production  of  crude  petroleum  there  is  being  rapidly  increased,  and 
the  oil  is  better  suited  by  its  quality  for  fuel  than  for  refining  pur- 
poses, owing  to  the  small  proportion  of  volatile  constituents  and  large 
proportion  of  heavy  hydrocarbons.  It  is  just  the  contrary  with  the 
petroleum  found  in  the  Eastern  States,  which  is  especially  adapted  to 
the  manufacture  of  illuminating  oils,  owing  to  the  large  proportion 
of  volatile  hydrocarbons  it  contains. 

The  petroleum-fields  of  Peru  somewhat  resemble  those  of  Califor- 
nia, and  are  most  favorably  situated  close  to  the  sea.  The  crude  oil  is 
a  good  fuel  for  stationary  boilers,  and,  if  40  per  cent  of  benzene  and 
kerosene  are  distilled  off,  the  resulting  residuum  is  an  oil  of  about  22° 
B.  gravity  and  260°  to  280°  fire-test,  of  moderate  viscosity  and  con- 
taining no  paraffine.  It  preserves  its  fluidity  at  low  temperatures,  and 
makes  an  excellent  fuel  for  either  locomotive  or  marine  use.  The 
price  at  which  it  can  be  supplied  is  $5.00  to  $7.50  per  ton.  As  good 
eoal  on  the  west  coast  of  South  America  seldom  reaches  a  lower  figure 
than  $6.25  per  ton,  this  fuel-oil  will  be  able  to  compete  with  it  from 
an  economic  point  of  view  so  soon  as  a  sufficiently  large  supply  of  it 
is  guaranteed. 


FUELS  OTHER  THAN  COAL.  141 

Some  of  the  advantages  claimed  for  liquid  fuel  are : 

1.  Diminished  loss  of  heat  up  the  funnel,  owing  to  the  clean  con- 
dition the  tubes  can  be  kept  in,  and  to  the  smaller  amount  of  air 
which  has  to  pass  through  the  combustion-chamber  for  a  given  fuel 

consumption. 

2.  A  more  equal  distribution  of  heat  in  the  combustion-chamber, 
as  the  doors  do  not  have  to  be  opened,  and  consequently  a  higher  effi- 
ciency is  obtained. 

3.  With  oil  there  is  no  chance  of  getting  dirty  fires  on  a  hard  run, 
as  with  coal. 

4.  A  reduction  in  cost  of  handling  fuel,  since  in  one  case  it  is  all 
done  mechanically  or  by  gravitation,  while  with  solid  fuel  a  great  deal 
of  manual  labor  is  required. 

5.  No  firing  tools  or  grate-bars  are  used,  consequently  the  furnace 
lining  and  brickwork  floors,  etc.,  suifer  less  damage. 

6.  No  dust  nor  ashes  to  cover  or  fill  the  tubes  and  dimmish  the 
heating  surface,  nor  to  be  handled  or  carted  away. 

7.  Petroleum  does  not  suffer  while  being  stored,  while  the  deterio- 
ration of  coal  under  atmospheric  influence  is  well  known. 

8.  Ease  with  which  fire  can  be  regulated,  from  a  low  to  a  most 
intense  heat  in  a  short  time. 

9.  Absence   of   sulphur  or  other  impurities   and  longer  life  of 
plates,  etc. 

10.  Lessening  of  manual  labor  to  fireman. 

11.  Great  increase  of  steaming  capacity,  as  was  conclusively  proved 
when  many  factories  returned  to  coal  in  Pennsylvania  and  Ohio;  they 
had  to  increase  their  boiler  capacity  about  35  per  cent. 

The  coal  consumption  of  the  world  is  probably  in  the  neighbor- 
hood of  600,000,000  tons  per  annum,  while  that  of  petroleum  is  only 
about  17,000,000  tons,  of  which  by  far  the  greatest  part  is  used  for 
illuminating  or  lubricating  purposes;  so  the  amount  of  petroleum 
available  for  fuel  purposes  is  probably  not  more  than  1  per  cent  of  the 
coal  used.  Liquid  fuel  will  therefore  never  be  used  very  extensively 
as  compared  with  coal,  but  where  it  is  used  it  will  have  many  advan- 
tages over  the  solid  fuel.  On  vessels  of  war,  and  especially  torpedo- 
boats,  it  would  give  the  very  best  results  if  used  intelligently. 

Oil  vs.  Coal  as  Fuel. — A  test  by  the  Twin  City  Rapid  Transit  Com- 
pany of  Minneapolis  and  St.  Paul  showed  that  with  the  ordinary  Lima 
oil  weighing  6  T6^  pounds  per  gallon,  and  costing  2^  cents  per  gallon, 
and  coal  that  gave  an  evaporation  of  7^  Ibs.  of  water  per  pound  of  coal, 


STEAM-BOILER  ECONOMY. 

the  two  fuels  were  equally  economical  when  the  price  of  coal  was  $3.85 
per  ton  of  2000  Ibs.  With  the  same  coal  at  $2.00  per  ton,  the  coal 
was  37 f0  more  economical,  and  with  the  coal  at  $4. 85  per  ton,  the  coal 
was  20$  more  expensive  than  the  oil.  These  results  include  the 
difference  in  the  cost  of  handling  the  coal,  ashes,  and  oil.* 

In  1892  there  were  reported  to  the  Engineers'  Club  of  Philadelphia 
some  comparative  figures,  from  tests  undertaken  to  ascertain  the  rela- 
tive value  of  coal,  petroleum,  and  gas. 

Lbs.  Water,  from 
and  at  212°  F. 

1  Ib.  anthracite  coal  evaporated 9.70 

1  Ib.  bituminous  coal 10.14 

1  Ib.  fuel  oil,  36°  gravity 16.48 

1  cubic  foot  gas,  20  C.  P 1.28 

The  gas  used  was  that  obtained  in  the  distillation  of  petroleum, 
having  about  the  same  fuel  value  as  natural  or  coal-gas  of  equal 
candle  power. 

Taking  the  efficiency  of  bituminous  coal  as  a  basis,  the  calorific 
energy  of  petroleum  is  more  than  60$  greater  than  that  of  coal; 
whereas,  theoretically,  petroleum  exceeds  coal  only  about  45$ — the 
one  containing  14,500  heat-units,  and  the  other  21,000. 

Comparative  tests  of  crude  petroleum  and  of  Indiana  block  coal  for 
steam-raising  at  the  South  Chicago  Steel  Works  f  showed  that,  with 
coal,  14  tubular  boilers  16  ft.  X5  ft.  required  25  men  to  operate  them; 
with  fuel  oil,  6  men  were  required,  a  saving  of  19  men  at  $2  per  day, 
or  $38  per  day. 

For  one  week's  work  2731  barrels  of  oil  were  used,  against  848 
tons  of  coal  required  for  the  same  work,  showing  3.22  barrels  of  oil  to 
be  equivalent  to  1  ton  of  coal.  With  oil  at  60  cents  per  barrel  and 
coal  at  $2.15  per  ton,  the  relative  cost  of  oil  to  coal  is  as  $1.93  to 
$2.15.  No  evaporation  tests  were  made. 

Gas  Fuel. — Natural  gas  is  an  ideal  fuel  for  steam-boilers  wherever 
it  can  be  obtained  in  sufficient  quantity  and  at  reasonable  cost  as 
compared  with  coal.  About  1890  it  was  in  quite  general  use  in 
western  Pennsylvania  and  in  many  places  in  Ohio  and  Indiana,  when 
numerous  wells  furnished  vast  quantities  of  gas  at  a  high  pressure, 
but  in  a  few  years  the  supply  diminished  and  it  became  too  high  in 

*  Iron  Age,  Nov.  2,  1893. 

f  Trans.  A.  I.  M.  E.,  xvii.  p.  807. 


FUELS  OTHER   THAN  COAL. 


143 


Ohio. 

,       ,  Indiana    » 

Find- 
lay. 

St. 
Mary's. 

Muncie. 

Ander- 
son. 

Koko- 
mo. 

Marion. 

1.64 

1.94 

2.35 

1.86 

1.42 

1.20 

93.35 

93.85 

92.67 

93.07 

94.16 

93.57 

.35 

.20 

.35 

.47 

.30 

.15 

.41 

.44 

.45 

.73 

.55 

.60 

.25 

.23 

.25 

.26 

.29 

.30 

.39 

.35 

.35 

.42 

.30 

.55 

3.41 

2.98 

3.53 

3.02 

2.80 

3.42 

.20 

.21 

.15 

.15 

.18 

.20 

price  to  be  commonly  used  in  steam-boilers.     Its  use  is  now  confined 
chiefly  to  household  purposes.     The  following  are  some  analyses :  * 

NATURAL  GAS  IN   OHIO  AND  INDIANA. 

t  ' 
Description.  £j£. 

Hydrogen , ...     1.89 

Marsh-gas 92.84 

defiant  gas 20 

Carbon  monoxide 55 

Carbon  dioxide. .....       .20 

Oxygen 35 

Nitrogen 3.82 

Hydrogen  sulphide  . .       .15 

Approximately  30,000  cubic  feet  of  gas  has  the  heating  power  of 
one  ton  of  coal. 

Producer-gas. — Since  the  invention  of  the  Siemens  producer  and 
regenerative  furnace,  in  1856,  and  their  general  introduction  into 
metallurgical  and  glass  works,  many  attempts  have  been  made  to  use 
producer-gas  as  a  fuel  for  steam-boilers,  the  evident  advantage  being 
the  ease  of  conveying  the  gas  in  pipes  from  a  centrally-located  pro- 
ducer-plant to  a  number  of  boilers,  the  facility  of  operation  of  the 
boilers  with  gaseous  fuel,  and  the  saving  of  labor.  These  attempts 
have  generally  failed,  however,  on  account  of  the  facts  that  the  gas- 
making  process  always  entailed  some  loss  of  heat,  that  the  producers 
were  of  too  great  cost,  and  that  it  was  difficult  to  drive  them  at  the 
varying  rates  usually  required  in  steam-boiler  practice.  The  follow- 
ing analysis  of  producer-gas  is  given  by  W.  II.  Blauvelt :  f 

PRODUCER-GAS  FROM  ONE  TON  OF  COAL. 

Analysis  by  Volume.    Per  Ct.    Cubic  Feet.       Pounds.  Equal  to— 

CO 25.3      33,213.84      2451.20      1050.51  Ibs.  C  +  1400.7  Ibs.  0. 


H  . 

9.2 

12,077.76 

63.56 

63.56    ' 

H. 

CH4  

3.1 

4,069.68 

174.66 

174  66    ' 

CH4. 

C2H4  

0.8 

1,050.24 

77.78 

77.78    ' 

C2H4. 

CO  

3.4 

4,463.52 

519.02 

141.54    ' 

C  +  377.44  Ibs. 

O. 

N  (by  difference).  . 

58.2 

76,404.96 

5659.63 

7350.17    ' 

Air. 

100.0 

131,280.00 

8945i85 

Calculated  upon  thia  basis,  the  131,280  ft.  of  gas  from  the  ton  of 
coal  contained  20,311,162  B.T.U.,  or  155  B.T.U.  per  cubic  foot,  or 
2270B.T.U.  perlb. 


*  Engineering  and  Mining  Journal,  April  21,  1894. 
t  Trans.  A.  I.  M.  E.,  xviii.  p.  614. 


CO...  

Natural 
Gas. 

0.50 

Coal- 
gas. 

6.0 

Water- 
gas. 

45.0 

H  

2.18 

46.0 

45.0 

CH4              

92.6 

40.0 

3.0 

C2H4. 

0.31 

4.0 

C02  

0.26 

0.5 

4.0 

N  

3.61 

1.5 

2.0 

o  

0.34 

05 

0.5 

1.5 

1.5 

Pounds  in  1000  cubic  feet  .  .  . 
Heat-units  in  1000  cubic  feet 

45.6 
1,100,000 

32.0 
735,000 

45.6 
322,000 

144:  STEAM-BOILER  ECONOMY. 

The  composition  of  the  coal  from  which  this  gas  was  made  was  as 
follows:  Water,  1.26$;  volatile  matter,  36.22$;  fixed  carbon,  57.98$; 
sulphur,  0.70$;  ash,  3.78$.  One  ton  contains  1159.6  Ibs.  carbon 
and  724.4  Ibs.  volatile  combustible,  the  energy  of  which  is  31,302,200 
B.T.U.  Hence,  in  the  processes  of  gasification  and  purification  there 
was  a  loss  of  35.2$  of  the  energy  of  the  coal. 

The  following  table  of  comparative  analyses  and  heating  values  of 
different  kinds  of  gas  is  given  by  W.  J.  Taylor:  * 

Producer-gas. 
Anthra.     Bitumin. 
27.0          27.0 
12.0          12.0 
1.2  2.5 

0.4 

2.5  2.5 

57.0          56.2 
03  0.3 

esie          65.9 
137,455    156,917 

Corn  as  Fuel. — It  is  quite  common  in  Nebraska,  in  years  when  the 
corn  crop  is  abundant  and  selling  prices  low,  to  use  corn  instead  of 
coal  as  fuel.  Prof.  C.  K.  Richards  reports  in  Cassier's  Magazine  the 
results  of  two  boiler  tests,  one  with  corn  and  one  with  good  Rock 
Springs  bituminous  coal,  costing  in  Lincoln,  Neb.,  $6.65  per  ton. 
The  results  showed  that  the  coal  gave  1.9  times  as  much  heat  per  Ib. 
as  the  corn.  Tests  of  both  fuels  in  a  fuel  calorimeter  gave  7076 
B.T.U.  for  the  corn,  and  13,010  for  the  coal,  a  ratio  of  1  to  1.86. 
Other  calorimeter  tests  of  different  sample  of  corn  gave  results  as  fol- 
lows: 

THE   HEATING  VALUE  OF  CORN. 

Heating  Value  in  B.T.U. 

Per  Ib.  of       Per  Ib.  of  Dry       Per  Ib.  of  Dry 
Kind  of  Material.  Material.  Material.  Combustible. 

Yellow  Dent  corn  and  cob 8040  

Yellow  Dent  corn ..  8202  8959  9085 

Yellow  Dent  cob 7214  7841  7958 

White  Dent  corn  and  cob 7841  

White  Dent  corn 8382  9199  9301 

White  Dent  cob 7571  8174  8285 

Assuming  the  average  heating  value  of  Nebraska  coal  at  11,500 
B.T.U.  per  lb.2  that  of  corn  8040  B.T.U.,  and  the  weight  of  corn  56 
Ibs.  per  bushel,  corn  at  10  cents  per  bushel  would  be  as  cheap  a  fuel 
as  coal  at  $5.11  per  ton  of  2000  Ibs. 

*  Trans.  A.  I.  M.  E.,  xviii.  p.  205. 


CHAPTEE  VII. 

FURNACES.  —  METHODS    OF   FIRING.  — SMOKE-PREVENTION.— ME- 
CHANICAL   STOKERS.— FORCED    DRAFT. 

Location  of  the  Furnace, — The  furnace,  or  fire-box,  of  a  steam- 
boiler  should  be  considered  as  an  apparatus  separate  and  distinct  from 
the  boiler  itself.  The  function  of  the  furnace  is  to  generate  heat  by 
the  combustion  of  the  fuel;  that  of  the  boiler  is  to  transfer  the  heat 
into  the  water.  The  combustion-chamber,  when  there  is  one,  is  an 
extension  of  the  fire-box;  its  office  is  to  afford  space  in  which  to  com- 
plete the  combustion  of  the  volatile  gases  which  are  imperfectly 
burned  in  the  fire-box. 

In  internally  fired  boilers,  such  as  the  locomotive,  marine,  Lanca- 
shire, and  vertical  tubular  boilers,  the  fire-box  is  located  inside  of  the 
boiler.  The  chief  advantage  of  this  method  of  construction  is  its  econ- 
omizing of  space,  but  it  is  attended  with  the  disadvantages  of  limit- 
ing the  area  of  grate-surface,  and  thereby  limiting  the  coal-burning 
capacity  of  the  boiler,  and,  with  soft  coal,  of  providing  insufficient 
space  for  a  combustion-chamber,  in  which  to  burn  the  volatile  gases. 
Another  objection  to  the  internal  furnace  is  usually  that  the  walls  of 
the  fire-box  and  combustion-chamber  are  metallic  surfaces,  kept  com- 
paratively cool  by  the  water  in  the  boiler,  which  chill  the  gases  and 
tend  to  prevent  their  combustion.  In  some  such  furnaces,  however, 
fire-brick  arches  or  walls  are  used,  which  have  the  beneficial  effect  of 
keeping  the  furnace  at  a  high  temperature. 

With  other  types  of  boilers,  such  as  the  horizontal  tubular  and  the 
common  form  of  water-tube  boiler,  with  inclined  tubes,  it  is  customary 
to  locate  the  furnace  immediately  underneath  the  boiler,  between  the 
brick  walls  of  the  setting.  For  horizontal  tubular  boilers  this  method 
of  setting  is  usually  satisfactory,  for  the  width  between  the  side-walls 
of  the  setting  is  sufficient  to  accommodate  an  ample  area  of  grate-sur- 
face, on  which  may  be  burned,  at  moderate  rates  of  combustion,  all 
the  coal  that  should  be  burned  for  the  amount  of  heating  surface  of 

145 


146  STEAM-BOILER  ECONOMY. 

the  boiler.  When  soft  coal  is  used  this  setting  allows  of  a  long  travel 
of  the  gases,  which  is  favorable  to  their  combustion,  and  furthermore, 
it  furnishes  sufficient  space  in  which  to  build  fire-brick  arches,  baffle- 
walls,  or  other  devices  to  more  perfectly  secure  complete  combustion. 

With  water-tube  boilers  of  the  inclined-tube  form,  this  location  is 
unobjectionable  when  large  sizes  of  anthracite  coal  are  used;  in  this 
case  the  grate-surface  is  sufficiently  large  to  burn  with  moderate  draft 
all  the  coal  that  is  required  to  develop  the  full  economical  capacity  of 
the  boiler,  and  the  small  quantity  of  volatile  gases  is  easily  burned  in 
the  fire-box.  With  small  sizes  of  coal  this  setting  does  not  provide 
sufficient  space  for  grate-surface  enough  to  develop  the  usual  rated 
capacity  of  the  boiler,  unless  a  very  strong  draft  is  provided  either  by 
a  tall  chimney  or  by  mechanical  means.  The  fine  sizes  of  anthracite 
usually  contain  a  considerable  percentage  of  moisture,  which  forms 
combustible  gas  by  its  decomposition  by  red-hot  carbon,  some  of  which 
gas  is  apt  to  escape  unburned  unless  abundant  room  is  provided  for 
burning  it  in  the  fire-box. 

For  bituminous  coal  the  ordinary  setting  of  an  inclined  water-tube 
boiler,  with  the  gas-passages  rising  immediately  above  the  furnace  into 
the  nest  of  tubes  above,  is  entirely  unsuitable.  There  is  insufficient 
room  in  the  furnace  for  the  burning  of  the  gases  ;  they  are  chilled  by 
the  water-tubes  above  the  furnace;  they  deposit  soot  upon  them,  dimin- 
ishing the  effectiveness  of  the  heating  surface,  and  a  large  proportion 
of  the  gas  escapes  unburned.  A  furnace  which  provides  a  long  travel 
of  the  gases  under  a  fire-brick  roof,  before  they  are  allowed  to  enter 
the  nest  of  tubes,  such  as  the  setting  of  the  Heine  boiler,  is  an  im- 
provement in  this  respect,  but  such  a  furnace  is  not  well  adapted  to 
boilers  having  more  than  seven  horizontal  rows  of  tubes,  for  in  this 
case  the  gas-passage  along  the  tubes  is  of  too  large  an  area  in  cross- 
section  to  cause  the  current  of  hot  gas  to  completely  envelop  all  the 
tubes,  and  it  therefore  allows  of  "short-circuiting,"  rendering  some  of 
the  heating  surface  ineffective. 

External  fire-brick  furnaces,  commonly  called  "  Dutch  ovens,"  are 
•used  with  the  vertical  types  of  water- tube  boilers,  and  to  some  extent 
with  the  inclined-tube  boilers,  with  great  advantage.  When  properly 
designed  they  admit  of  sufficient  areas  of  grate-surface,  and  of  the  use 
of  deflecting  arches,  baffle-walls,  etc.,  for  insuring  combustion  of  the 


Requirements  of  a  Good  Furnace. — (1)  It  should  have  ample  coal- 
burning  capacity.     It  should  be  able  to  burn  the  amount  of   coal 


FURNACES.— METHODS  OF  FIRING,  ETC.  147 

needed  to  generate  the  maximum  quantity  of  steam  that  may  be  re- 
quired during  any  hour  of  the  day,  under  the  most  unfavorable  condi- 
tions that  may  be  expected,  such  as  atmospheric  or  other  conditions 
tending  to  diminish  the  chimney  draft,  and  coal  of  a  poorer  quality 
than  is  usually  furnished. 

(2)  The  grates  should  be  of  such  a  kind  that  ash  and  clinker  may 
be  easily  removed  from  them  without  stopping  the  operation  of  the 
boiler  for  more  than  a  few  minutes  at  a  time,  and  the  bars  should  be  so 
spaced  that  coal  is  not  apt  to  be  wasted  by  falling  through  them. 

(3)  It  should  be  so  constructed  as  to  be  capable  of  burning  thor- 
oughly all  of  the  gases  that  may  be  distilled  from  the  fuel  before  they 
come  in  contact  with  the  comparatively  cool  heating  surfaces  of  the 
boiler. 

(4)  It  should  be  durable,  free  from  breakdowns  of  coal-feeding  ap- 
pliances or  shaking  grates,  and  from  melting  down  of  fire-brick  arches. 

(5)  Furnaces  of  externally  fired  boilers  should  be  built  with  thick 
walls,  so  as  to  minimize  as  far  as  possible  loss  of  heat  by  radiation,  or 
preferably  with  double  walls  with  air-spaces  between.     The  air-spaces 
may  with  advantage  be  so  arranged  as  to  cause  a  current  of  air  to  flow 
through  them  into  the  ash-pit  or  above  the  fire. 

Burning  of  Anthracite  Coal. — For  large  sizes  of  anthracite,  such  as 
egg,  almost  any  kind  of  furnace  is  suitable,  and  no  great  degree  of  skill 
is  needed  to  fire  the  coal  so  as  to  obtain  the  best  results.  With  all 
ordinary  proportions  of  grate  and  heating  surface  a  moderate  draft  suf- 
fices to  burn  enough  coal  to  drive  the  boiler  up  to  and  beyond  its  eco- 
nomical rating.  Hand-firing  is  always  used  with  this  coal,  and  all  that 
the  fireman  needs  to  do  is  to  keep  a  level  bed  of  coal  on  the  grate  of  a 
depth  proportionate  to  the  force  of  the  draft,  to  watch  carefully  to 
prevent  the  formation  of  air-holes  in  the  bed  of  coal,  and  to  clean  the 
fire  at  long  intervals  of  time,  say  from  six  to  ten  hours.  When  there 
is  plenty  of  draft  the  fireman  has  control  of  two  factors  governing  the 
combustion,  viz.,  the  damper  and  the  thickness  of  the  bed  of  coal, 
which  he  can  regulate  at  his  pleasure.  With  a  given  force  of  draft, 
which  may  be  controlled  by  the  damper,  if  the  bed  of  coal  is  too 
thin  an  excessive  supply  of  air  passes  through  it,  causing  a  waste  of 
neat  in  the  chimney  gases;  if  it  is  too  thick  some  of  the  carbon 
will  be  burned  only  to  carbon  monoxide,  instead  of  to  carbon  dioxide, 
causing  a  great  loss  of  heat.  The  latter  source  of  loss,  when  there  is 
sufficient  draft  available,  may  easily  be  prevented,  for  it  makes  itself 
known  by  a  sluggish  action  of  the  fire,  the  presence  of  blue  flames  on 


148  STEAM-BOILER  ECONOMY. 

the  bed  of  coal,  and  low  temperature  of  the  furnace.  The  remedy  is 
either  to  carry  a  thinner  bed  of  fire,  or  to  open  the  damper  and  give  a 
stronger  draft  in  the  furnace.  The  loss  due  to  excess  of  air  on  account 
of  too  thin  a  bed  of  coal  is  much  more  common,  and  its  effect  in  the 
furnace  is  not  so  apparent  to  the  fireman.  It  may  be  prevented  by 
carrying  as  thick  a  bed  of  coal  as  will  not  cause  the  temperature  of  the 
furnace  to  be  visibly  lowered  and  blue  flames  to  make  their  appearance. 

In  all  cases  the  highest  possible  temperature  of  the  furnace 
gives  the  highest  economy,  provided  the  heating  surface  is  of 
sufficient  extent  to  absorb  the  proper  proportion  of  the  heat  generated, 
and  to  cool  the  gases  to  the  lowest  practicable  temperature  before  they 
reach  the  chimney -flue.  The  highest  temperature  is  obtained  by  firing 
small  quantities  of  coal  at  a  time  and  by  keeping  the  bed  of  coal  at 
such  a  thickness  as  will  insure  complete  combustion  without  an  exces- 
sive supply  of  air  passing  through  it. 

With  small  sizes  of  anthracite  there  is  more  difficulty  in  securing 
the  best  conditions  of  combustion.  The  fineness  of  the  coal  tends  to 
choke  the  air-passages  through  the  bed  on  the  grate,  and  a  thinner  bed 
has  therefore  to  be  carried  unless  there  is  a  very  strong  draft,  and  a  thin 
bed  is  more  difficult  than  a  thick  one  to  keep  free  of  air-holes.  The 
coal  is  usually  much  higher  in  ash  than  large-sized  coal,  and  the  fires 
therefore  need  to  be  cleaned  oftener— an  operation  which  always  chills 
the  fire,  decreases  the  rate  of  steaming,  and  causes  a  waste  of  heat.  The 
evaporation  per  pound  of  combustible  with  fine  sizes  of  coal  is  usually 
in  ordinary  practice  considerably  less  than  with  egg  coal. 

In  order  to  burn  a  sufficient  quantity  of  fine  sizes  of  anthracite 
coal  to  develop  the  required  capacity  of  a  boiler  it  is  common  to  use  a 
forced  blast  provided  either  by  a  fan  or  by  a  steam-jet. 

Burning  Small  Sizes  of  Anthracite. — The  report  of  the  Pennsyl- 
vania State  Commission  on  "  Waste  of  Coal  Mining/'  1883,  contains 
the  following: 

A  number  of  experiments  were  made  in  the  testing  laboratory  of 
Coxe  Bros.  &  Co.,  by  Mr.  John  R.  Wagner,  in  burning  small  coals 
with  a  forced  draught,  obtained  in  one  case  by  a  fan  and  in  the  other 
by  a  steam-jet.  They  showed : 

"First. — That  the  ashes  produced  by  a  steam-jet  were  never  as 
low  in  carbon  as  those  produced  by  the  fan ;  that  is,  an  appreciably 
larger  per  cent  of  the  carbon  was  utilized  by  the  fan-blast.  This  ap- 
pears to  be  due  to  the  fact  that  when  the  carbon  in  the  ash  over  the 
grate  is  reduced  to  a  certain  point  the  steam  dampens  it  somewhat, 
and  it  ceases  to  burn  sooner  than  it  does  when  dry  air  only  is  blown 
through  it. 


FURNACES.— METHODS  OF  FIRING,  ETC.  149 

"Second. — That  with  the  fan-blast  the  rate  of  combustion  per 
square  foot  per  hour  is  greater  than  with  the  steam- jet. 

"  Third. — It  was  found  that  where  a  bed  of  coal  was  ignited  and 
burned  out,  the  percentage  of  carbon  in  the  ash  is  much  less  than 
where  coal  is  successively  added  to  the  burning  mass.  In  practice 
it  is  not  generally  possible  to  allow  the  bed  to  burn  out  sufficiently 
before  adding  the  cold,  unignited  coal ;  the  result  is  a  damping  down 
of  the  fire,  which  causes  the  ash  to  cease  burning  sooner  than  it  would 
do  if  there  were  no  reduction  of  temperature  and  checking  of  the 
draught  due  to  the  adding  of  the  coal. 

"Fourth. — There  seems  to  be  no  doubt  that  the  introduction  of 
steam  into  the  ash-pit  decreases  very  materially  the  tendency  of  the 
coal  to  clinker  on  the  grate  in  comparison  with  the  fan-blast  or  natu- 
ral draught.  It  also  changes  the  color,  volume,  and  character  of  the 
ilame,  and,  owing  to  producer  action,  increases  the  distance  that  the 
flame  extends  beyond  the  bridge-wall.  In  many  cases  it  is  not  prac- 
tical, or  at  least  it  is  very  difficult,  to  fire  the  smaller  sizes  of  coal 
without  the  steam-jet  on  account  of  the  clinkering.  This  effect  of 
steam  on  clinkering  is  probably  due  to  the  fact  that  the  steam,  to  a 
certain  extent,  moistens  the  ash  close  to  the  grate  and  prevents  the 
ash  from  reaching  there  as  high  a  temperature  as  it  would  with  dry 
air.  It  is  also  probable  that  the  decomposition  of  the  steam  into  car- 
bonic oxide  and  hydrogen,  which  takes  place  to  a  certain  extent,  and 
which,  of  course,  is  accompanied  by  a  reduction  of  temperature,  tends 
to  prevent  clinkering.  The  decomposition  of  the  steam,  accompanied 
by  the  formation  of  carbonic  oxide  and  hydrogen,  will  probably  ac- 
count for  the  difference  in  the  flame  referred  to. 

"Fifth. — A  careful  study  of  the  burning  of  culm,  that  is,  the 
burning  of  small  coals  with  more  or  less  dust  in  them,  in  these  and 
other  experiments,  seemed  to  show  that  in  almost  all  cases  it  is  accom- 
panied by  a  very  high  percentage  of  carbon  in  the  ash,  which  analysis 
showed,  in  some  cases,  reached  58  per  cent.  Unless  special  precau- 
tions are  taken  to  prevent  it,  a  large  portion  of  the  fine  coal  runs 
down  through  the  grate.  When  the  culm  gets  red  hot  it  acts  almost 
like  dry  sand  and  works  its  way  into  the  ash-pit,  thus  increasing 
largely  the  percentage  of  carbon.  Where  coal  has  to  be  transported 
any  distance,  the  value  of  the  culm  at  the  mines  being  very  small,  it 
is  probable,  from  the  investigations  made,  that  it  would  be  cheaper  to 
remove  the  dust  and  transport  only  the  larger  coal. 

"Sixth. — It  has  been  found  that  the  percentage  of  iron  pyrites, 
which  occurs  to  a  greater  or  less  extent  in  all  coals,  increases  very 
rapidly  with  the  smallness  of  the  coal.  This  is  due  to  the  fact  that 
the  iron  pyrites  occur  generally  in  thin  layers  or  in  incrustations  on 
the  coal.  These  thin  layers  are  broken  off  and  pulverized  in  the 
preparation  and  handling  of  the  coal,  and  are  therefore  found  to  a 
much  greater  extent  in  the  very  small  coal.  It  is,  of  course,  well 
known  that  the  presence  of  iron  pyrites  in  fuel  is  very  undesirable,  as 
it  generates  sulphurous  acid  and  has  a  tendency  to  destroy  the  grates 


150 


STEAM-BOILER  ECONOMY. 


or  other  iron-work  around  the  boilers,  besides,  in  many  cases,  increas- 
ing the  tendency  to  clinker. 

"Seventh. — That  while  the  fan-blast  produces  the  best  ash  and 
gives  a  more  perfect  and  greater  rate  of  combustion,  yet  in  many  cases 
it  is  more  advantageous  to  use  the  steam-blower  on  account  of  the 
clinkering,  which  may  cause  very  serious  trouble.  In  certain  locali- 
ties, particularly  in  cities,  the  noise  of  the  steam-blower  is  sometimes 
a  disadvantage. 

"Eighth. — While  it  is  not  positively  demonstrated,  it  is  thought 
that  the  question  of  mixing  small  coals  from  different  veins  of  differ- 
ent localities  is  a  matter  of  importance.  It  would  appear  that  some- 
times two  coals,  each  of  which,  when  burned  separately,  give  reason- 
ably satisfactory  results,  when  mixed  together,  clinker  and  give  trou- 
ble, probably  because  the  ash  of  the  combined  coals  forms  a  much 
more  fusible  silicate  than  either  of  the  ashes  separately. 

"  Ninth. — It  would  seem  that  the  combustion  of  the  small  anthra- 
cite is  more  perfect  when  the  coal  remains  undisturbed,  or  as  nearly 
as  possible  in  the  condition  in  which  it  was  put  in  the  fire,  instead  of 
being  turned  over  so  that  the  partially  consumed  and  the  unconsumed 
coal  are  mixed  together." 

Comparative  Efficiency  of  Steam-  and  Fan-blowers. — The  following 
record  of  comparative  tests  of  steam-  and  fan-blowers,  made  on  three 


Dimensions  of  boilers                          36  in  diain    42  ft  long. 

With  Steam- 

With  Fan- 

Area  grate-surface  3  boilers               61  5  SQ  ft 

blower 

COAL. 

7,700  Ib. 

6,100  Ib. 

lotal  coal  burned  (less  mois  ure;  . 

1,330  " 

1,027  " 

6,370  " 

5,073  " 

17.2  per  cent 

16.8  per  cent 

962.5  Ib. 

762.5  Ib. 

L/oai  DU  ^n^a  Per      I    "  "  ii*  

796.3  " 

634.1   " 

WATER. 

39,241  Ib. 

34,890  Ib. 

5,444   " 

4,867     ' 

Water  evaporated  per  hour  per  Ib.  of  coal,  actual  conditions.  .  . 
"                "             "      "        "    "     "  coal  from  and  at  212°  .... 
"               "            "      "        "    "    "  combustible  from  and  at 
212°                             .... 

5.10   " 
5.66  " 

6.84   " 

5.59    * 
6.38    ' 

7.67    ' 

157.81    " 

141.1      ' 

Average  boiler  pressure                              

78    ' 

134° 

137° 

BLOWERS. 
Boiler  H  P  used  by  blowers  per  hour  from  and  at  212°  

11.9  H.  P. 

5.64  H.  P. 

Per  cent  of  the  developed  H.  P.  of  the  three  boilers  used  for 

7.4  per  cent 

4  per  cent 

2,502  ft. 

3,506  ft. 

.44  in 

.52  in. 

Horsepower  in  air  

0.1  73  H.  P. 

0.28  H.  P. 

REMARKS.— In  the  test  with  the  fan-blower,  the  exhaust  from  the  fan-engine  was  turned  into 
the  air-current  and  found  sufficient  to  keep  the  grates  free  from  clinker. 

Average  steam-pressure  at  steam-blowers. 74  Ib. 

"       I.  H.  P.  of  fan-engine 1.62  H.  P. 

No.  of  revolutions  of  fan-engine 160  revs. 

"         *'    "  "  "fan 915    " 

Useful  effect  of  fan 17* 


FURNACES.—  METHODS  OF  FIRING,  ETC. 


151 


plain  cylinder  boilers  at  the  Short  Mountain  Colliery,  Lykens,  Pa.,  was 
published  in  the  Colliery  Engineer,  August,  1897.  The  conditions  in 
each  case  were  the  same,  rice  coal  being  used  as  fuel  on  a  sectional 
grate  with  12  per  cent  air-openings. 

The  fan-blower  consisted  of  a  gangway-fan  33  in.  diam.,  4  paddles 
9x9^  in.,  driven  by  a  small  slide-valve  engine  with  cylinder  4T^  in. 
diam.,  7f-  in.  stroke.  Steam  was  supplied  by  a  small  upright  boiler  on 
which  an  evaporative  test  was  run  during  the  test  on  the  cylinder 
boilers. 

The  steam-blower  was  made  of  j-in.  pipe,  circle  6J  in.  diam.,  16 
holes,  tapered  -J  in.  outside,  T^  in.  inside,  diam.  Steam  was  supplied 
by  the  upright  boiler  on  which  a  test  was  run  as  above.  Duration  of 
each  test,  8  hours. 

The  saving  of  fuel  by  the  use  of  the  fan-blower,  as  compared  with 
the  steam-blower,  was  13.9  per  cent,  taking  into  account  the  steam 
used  by  each  blower. 

Grate-bars. — Two  styles  of  grate-bars  in  common  use  are  shown  in 
Figs.  12  and  13.  The  first  is.  a  plain  cast-iron  bar,  tapered  in  cross- 
section,  so  as  to  make  a  wider 
opening  between  the  bars  at 
the  lower  than  at  the  upper 
edge.  Projections  are  cast  on 
the  sides  of  the  bars  to  keep 
them  at  the  proper  distance 
apart.  The  second  is  channel- 
shaped  in  cross-section,  with  the  upper  surface  provided  with 
V-shaped  openings.  The  total  area  of  the  air-spaces  is  usually  made 
from  30  to  50  per  cent  of  the  total  area  of  the  grate-surface.  The 
width  of  the  air-spaces  and  of  the  bars  or  ribs  differs  according  to  the 


FIG.  12. 


TOP  AND  SIDE  VIEW. 


END  VIEW. 


FIG.  13. 


size  and  kind  of  coal  used.  For  fine  sizes  of  anthracite  the  spaces  are 
made  as  narrow  as  -|  inch.  For  large  sizes  of  anthracite  and  for  "  run- 
of-mine  "  soft  coal  they  are  often  made  as  wide  as  1  inch.  When  the 
ash  of  the  coal  tends  to  form  clinkers,  narrow  air-spaces  are  objection- 


152  STEAM-BOILER  ECONOMY. 

able,  as  they  are  apt  to  become  clogged,  and  are  difficult  to  keep  open 
so  as  to  allow  a  sufficient  supply  of  air  to  pass  through  them. 

The  resistance  to  the  passage  of  air  through  the  grate  and  the  bed 
of  coal  lying  upon  it  depends  upon  other  things  besides  the  size  of  the 
air-spaces  in  the  grate,  such  as  the  size  of  the  coal,  its  quality  as 
regards  coking  or  non-coking,  the  thickness  of  the  bed  of  coal  and 
ashes,  the  presence  or  absence  of  clinker,  etc.  With  coals  that  are 
low  in  ash,  and  the  ash  non-clinkering,  it  is  possible  to  burn  the  coal 
with  very  narrow  air-spaces  through  the  grates. 

Fine  sizes  of  anthracite  are  sometimes  burned  on  flat  cast-iron 
plates  perforated  with  tapering  holes  about  £  inch  diameter  at  the 
upper  surface,  the  total  air-space  being  about  25  per  cent  of  the  grate- 
area. 

Mr.  F.  A.  Scheffler  *  reports  a  test  in  which  grate-bars  of  the  form 
shown  in  Fig.  13  were  used,  with  the  air-spaces  only  about  ^  inch  wide, 
and  the  total  area  of  air-space  only  about  15  per  cent  of  the  grate-sur- 
face. The  coal  was  Pittsburg  run-of-mine.  With  a  draft  pressure  of 
'0.46  in  water  column,  the  rate  of  combustion  was  24.8  Ibs.  of  coal  per 
sq.  ft.  of  grate  per  hour,  a  rate  sufficient  to  drive  the  boiler  to  much 
above  its  rated  capacity. 

On  the  other  hand,  the  author  once  made  a  test  with  Illinois  coal 
containing  a  large  percentage  of  sulphur,  with  bars  of  the  same  type, 
the  air-spaces  being  £  inch  in  width  and  with  a  draft  of  0.4  to  0.5 
inch,  but  was  unable  to  maintain,  even  with  the  maximum  draft,  a 
rate  of  combustion  sufficient  to  develop  the  rated  capacity  of  the  boiler. 
In  this  case  the  ash  fused  into  a  glass,  which  ran  into  and  choked  the 
air-spaces. 

Shaking-  and  Dumping-grates. — With  coals  of  the  character  just 
described,  shaking-  or  dumping-grates  are  almost  a  necessity,  unless 
mechanical  stokers  are  used  in  preference.  Many  different  forms  of 
such  grates  are  in  the  market.  They  may  be  divided  into  three  gen- 
eral classes:  1.  Shaking- or  Rocking-grates;  2.  Dumping-grates;  3. 
Shaking-  and  Dumping-grates.  In  the  first  class  the  bars  are  usually 
divided  into  small  sections,  which,  by  means  of  rocking-bars  and 
levers,  are  given  an  oscillatory  or  reciprocating  motion,  which  causes 
the  ash  to  fall  through  between  the  sections.  In  the  second  class  the 
sections  are  made  larger,  and  when  the  fires  are  to  be  cleaned 
from  clinker  the  sections,  or  a  part  of  them,  such  as  those  covering 
one-quarter  of  the  whole  grate- area,  are  rocked  from  a  horizontal  into 

*  Trans.  A.  S.  M.  E.,  vol.  xv.  p.  503. 


FURNACES.— METHODS  OF FIRING,  ETC. 


153 


a  vertical  position,  thus  breaking  up  the  clinker  and  allowing  it  to  fall 
through  the  large  openings  thus  made.  In  the  third  class  the  sections 
are  provided  with  mechanism  by  which  either  the  shaking  or  the 
dumping  motion  may  be  given  at  will.  For  non-clinkering  coals 
the  first  and  third  classes  are  used,  and  for  clinkering  coals  the  second 
and  third. 

The  use  of  shaking-grates  usually  entails  a  loss  of  some  unburned 
coal  through  the  grates,  amounting,  with  the  most  careful  handling, 
to  from  1  to  3  per  cent  of  the  total  coal  used ;  but  this  loss  is  often 
more  than  offset  by  the  gain  due  to  the  more  complete  combustion 
which  is  obtained  when  the  air-supply  is  unrestricted  by  ash  and 
clinker. 

The  McClave  Grate  is  shown  in  Fig.  14.    The  rear  section  is  shown 


FIG.  14. — THE  MCCLAVE  GRATE. 

in  the  usual  position.     The  front  section  is  shown  with  the  bars  tilted 
up  for  breaking  the  clinker. 

Each  row  or  section  of  grate-bars  is  divided  into  a  front  and  rear 
series  by  means  of  two  separate  connecting-bars,  operated  by  twin  stub- 
levers  and  connecting-rods,  with  an  operating  handle  adapted  to  grasp 
either  one  or  both  of  the  levers  in  such  a  manner  that  the  front  and  rear 
series  may  be  operated  separately  or  together.  This  provides  for  clean- 
ing out  the  worst  kind  of  clinkers  without  wasting  the  unconsumed 
fuel  on  the  surface,  as  that  may  be  shoved  over  on  the  stationary  part 
while  the  clinkers  and  ashes  of  the  other  series  are  being  cut  through 
into  the  ash-pit. 

The  McClave  grate  is  extensively  used  for  burning  buckwheat, 
birdseye,  and  other  fine  sizes  of  anthracite  coal.  It  is  also  used  in  the 


154 


STEAM-BOILER  ECONOMY. 


coal  regions  for  burning  culm  or  the  refuse  of  the  mines.  Concern- 
ing the  use  of  culm  as  fuel  the  circular  of  the  manufacturers  of  the 
McClave  grate  says : 

"  In  the  anthracite  coal-fields  the  waste  product  of  the  mines,  com- 
monly called  culm,  has  proved  to  be  a  most  excellent  fuel  for  steam  pur- 
poses and  is  now  being  successfully  used  by  the  largest  manufacturers 
and  producers  in  the  coal  region.  The  cost  of  this  fuel  at  the  mines 
is  merely  nominal,  but  in  order  to  burn  it  successfully  it  should  con- 
tain at  least  50  per  cent  of  buckwheat  and  should  be  fresh  from  the 
mine,  for  when  the  buckwheat  is  nearly  all  screened  out  of  it,  or  when 
it  has  been  exposed  to  the  weather  for  any  considerable  length  of  time, 
it  is  comparatively  worthless  as  fuel.  Again,  it  will  not  pay  to  ship  it 
any  great  distance,  as  the  freight  on  culm  is  just  as  much  per  ton  as  it 
is  on  buckwheat  coal,  which,  for  steam  purposes,  is  a  much  better  fuel 
than  culm,  and  costs  at  the  mine  only  from  30  to  35  cents  per  ton 
more  than  culm. ' ' 

The  Argand  Steam-blower,  shown  in  Figs.  15  and  16,  is  commonly 
used  in  connection  with  the  McClave  grate.     It  delivers  a  large  volume 
of  air,  mixed  with  steam,  under  the  grate.     The  steam  is  delivered  to- 
the  blower  through  a  metal  ring,  perforated 
with  small  holes  on  the  edge  nearest  to  the 
ash-pit,     The  jets  of  steam  induce  a  strong 


FIG.  15. 


FIG.  16. 


current  of  air  which  is  blown  under  the  grate.  While  the  use  of  a  steam- 
jet  is  usually  the  most  wasteful  method  of  producing  draft,  it  has  certain 
advantages  over  a  dry-air  blast  for  the  burning  of  cheap  coals  high  in  ash. 
The  decomposition  of  the  steam  into  oxygen  and  hydrogen  by  the  hot 
carbon  in  the  bed  of  coal  is  a  cooling  process,  which  tends  to  prevent  the 
formation  of  clinker  on  the  grates.  The  heat  absorbed  by  this  decompo- 
sition is  again  generated  when  the  gases  are  burned  in  the  fire-chamber 
above  the  grate,  so  that  the  only  losses  due  to  the  use  of  steam  are  the 
cost  of  the  steam  itself  and  the  heat  required  to  superheat  it  to  the 
temperature  of  the  chimney  gases. 


FURNACES.— METHODS  OF  FIRING,  ETC.  155 

How  to  Burn  Soft  Coal. — Of  all  known  methods  of  burning  soft 
coal  the  worst  is  the  one  which  is  most  commonly  practised,  viz. :  that 
of  burning  it  in  a  common  furnace,  consisting  of  a  set  of  grate-bars 
and  a  space  of  contracted  dimensions  between  them  and  the  heating 
surface  of  the  boiler,  the  coal  being  fed  by  hand.  This  method  is 
suitable  for  anthracite  coal,  the  smaller  sizes  containing  much  sur- 
face moisture  perhaps  excepted,  but  when  used  for  bituminous  coal  it 
is  objectionable  both  on  account  of  smoke  and  on  account  of  loss  of 
economy.  The  objections  to  the  method  increase  the  farther  we  go 
west  from  the  anthracite  coal-fields  of  Pennsylvania,  being  least  with 
the  semi-bituminous  coals  of  Pennsylvania,  Maryland,  and  Virginia, 
and  increasing  as  we  go  westward  and  find  the  percentages  of  moisture 
and  of  volatile  matter  both  increasing. 

Objections  to  the  Common  Method. — The  reasons  for  the  difficulty 
in  obtaining  high  economy  from  the  bituminous  coals  when  hand-fired 
in  ordinary  furnaces  may  perhaps  be  understood  if  we  consider  the 
sequence  of  events  that  take  place  between  two  consecutive  firings,  at 
an  interval  of,  say,  five  or  ten  minutes  apart.  Suppose  that  just  before 
firing  fresh  coal  an  intensely  hot  bed  of  coke,  say  6  inches  deep,  is  lying 
upon  the  grate-bars.  Half  a  dozen  shovelfuls  of  coal,  much  of  it  of 
fine  size,  are  spread  evenly  over  the  bed.  The  first  thing  that  the  fine 
fresh  coal  does  is  to  choke  the  air-spaces  existing  through  the  bed  of 
coke,  thus  shutting  off  the  air-supply  which  is  needed  to  burn  the 
gases  produced  from  the  fresh  coal.  The  next  thing  is  a  very  rapid 
evaporation  of  moisture  from  the  coal,  a  chilling  process,  which  robs 
the  furnace  of  heat.  Next  is  the  formation  of  water-gas  by  the  chem- 
ical reaction,  C  +  HaO  =  CO  -f-  2H,  the  steam  being  decomposed, 
its  oxygen  burning  the  carbon  of  the  coal  to  carbonic  oxide,  and  the 
hydrogen  being  liberated.  This  reaction  takes  place  when  steam  is 
brought  in  contact  with  highly  heated  carbon.  This  also  is  a  chilling 
process,  absorbing  heat  from  the  furnaces.  The  two  valuable  fuel- 
gases  thus  generated  would  give  back  all  the  heat  absorbed  in  their 
formation  if  they  could  be  burned,  but  there  is  not  enough  air  in  the 
furnace  to  burn  them.  Admitting  extra  air  through  the  fire-door  at 
this  time  will  be  of  no  service,  for  the  gases  being  comparatively  cool 
cannot  be  burned  unless  the  air  is  highly  heated.  After  all  the  mois- 
ture has  been  driven  off  from  the  coal,  the  distillation  of  hydrocarbons 
begins,  and  a  considerable  portion  of  them  escapes  unburned,  owing 
to  the  deficiency  of  hot  air,  and  to  their  being  chilled  by  the  relatively 
cool  heating  surfaces  of  the  boiler.  During  all  this  time  great  volumes 


156  STEAM-BOILER  ECONOMY. 

of  smoke  are  escaping  from  the  chimney,  together  with  unburned  hy- 
drogen, hydrocarbons,  and  carbonic  oxide,  all  fuel-gases,  while  at  the 
same  time  soot  is  being  deposited  on  the  heating  surface,  diminishing  its 
efficiency  in  transmitting  heat  to  the  water.  At  length  the  distillation 
of  the  hydrocarbons  proceeds  at  a  slower  rate,  the  very  fine  coal  which 
at  first  obstructed  the  air-supply  is  partially  burned  away,  sufficient 
hot  air  comes  through  the  bed  of  hot  coke  to  burn  thoroughly  all  the 
gases,  and  such  a  balance  of  conditions  between  the  amount  of  gas 
generated  and  the  amount  of  air  supplied  exists  that  the  best  possible 
conditions  for  maximum  economy  are  obtained  and  the  chimney-gases 
are  then  smokeless.  Finally  the  gases  are  all  distilled,  and  a  bed  of 
coke  remains,  which,  as  long  as  it  is  thick  enough  with  relation  to  the 
air-supply,  will  burn  under  good  conditions  for  economy,  but  as  soon 
as  it  burns  down  low  and  the  air-spaces  become  large  enough  to  allow 
an  excessive  supply  of  air  into  the  furnace,  a  new  condition  of  poor 
economy  is  reached,  the  excess  of  air  passing  up  the  chimney  carrying 
away  heat  which  should  have  been  utilized  in  the  boiler. 

The  waste  of  fuel  is  not  the  only  loss  occasioned  by  the  prevalent 
wrongful  method  of  burning  soft  coal.  In  all  western  cities  the  de- 
preciation in  value  of  residence  property  in  the  vicinity  of  factories, 
the  cost  of  painting  and  repainting  of  houses  and  stores,  the  constant 
scrubbing  and  washing  to  remove  soot,  and  the  destruction  of  textile 
fabrics,  if  they  could  all  be  expressed  in  dollars  and  cents,  would 
amount  to  an  enormous  total. 

Smoky  Chimneys  not  Necessary. — All  of  the  loss  due  to  smoky 
chimneys  it  is  quite  possible  to  avoid,  by  the  use  of  well-known  and 
well-tried  appliances.  The  principles  which  govern  the  complete  and 
smokeless  combustion  of  bituminous  coal  are  simple  enough,  but  the 
application  of  these  principles  in  practice  has  hitherto  been  usually 
considered  to  involve  extra  cost  of  installation  of  a  boiler  plant,  extra 
cost  of  repairs,  and  extra  trouble.  The  fear  of  extra  cost  and  trouble, 
together  with  exceeding  conservatism  of  factory  owners  in  regard  to 
everything  connected  with  steam-boilers,  have  been  the  chief  obstruc- 
tions to  the  universal  use  of  smokeless  furnaces  in  our  western  States. 
These  obstructions  are,  however,  rapidly  being  removed.  Many  large 
concerns  have  recently  introduced  smokeless  furnaces,  not  to  abate  a 
nuisance,  but  to- save  fuel  and  labor,  and  within  a  very  few  years  it 
may  be  expected  that  their  use  will  be  almost  universal  in  large  boiler 
plants. 

How  to  Avoid  Smoke. — Coal  can  be  burned  without  smoke,  pro- 
vided : 


FURNACES.— METHODS  OF  FIRING,  ETC.  157 

I.  The  gases  are  distilled  from  the  coal  slowly. 

II.  That  the  gases  when  distilled  are  brought  into  intimate  con- 
tact with  very  hot  air. 

III.  That  they  are  burned  in  a  hot  fire-brick  chamber. 

IV.  That  while  burning  they  are  not  allowed  to  come  in  contact 
with  comparatively  cool  surfaces,  such  as  the  shell  or  tubes  of  a  steam- 
boiler;  this  means  that  the  gases  shall  have  sufficient. space  and  time  in 
which  to  burn  before  they  are  allowed  to  come  in  contact  with  the 
boiler  surfaces. 

Practical  Success  of  Smoke-prevention. — Mr.  Alfred  E.  Fletcher, 
Chief  Inspector  of  the  Local  Government  Board  in  Scotland,  in  his 
report  for  1892,  says  : 

"  This  problem  of  combating  the  smoke  nuisance  must  be  carried 
on  like  other  struggles  by  attacking  the  weaker  part  first,  and  in  this 
case  it  is  the  black  part  of  the  smoke.  Although  this  part  of  the 
problem  is  not  easy,  yet  it  is  possible  of  solution,  and  has  been  in  many 
ways  successfully  attacked  as  far  as  the  smoke  of  factories  is  con- 
cerned. 

"  In  my  report  for  the  year  1888,  I  gave  an  account  of  experiments 
undertaken  in  this  cause.  I  there  detailed  the  result  of  the  examination 
of  the  smoke  from  52  furnaces  taken  indifferent  parts  of  the  country, 
where  various  kinds  of  coal  were  burnt,  and  in  different  forms  of  fur- 
nace. The  analyses  of  the  gases  of  combustion  showed  that  there  were 
great  differences  in  the  proportions  of  air  admitted,  and  that  in  all 
cases,  even  where  the  smoke  was  blackest,  there  was  an  excess  of  air. 
That  the  imperfection  of  the  combustion  did  not  arise  from  want  of 
air  in  the  fire,  but  from  a  misuse  of  it.  It  is  obvious  that  unless  the 
air  is  mixed  with  the  carbonaceous  gases,  combustion  is  impossible,  and 
also  unless  that  mixture  is  maintained  at  a  sufficiently  high  tempera- 
ture. In  short,  as  has  been  often  pointed  out,  there  must  be,  firstly, 
a  sufficiency  of  air;  secondly,  that  air  must  be  brought  into  contact 
with  the  fuel,  both  solid  and  gaseous,  and  thirdly,  the  mixture  of 
the  gases  and  the  air  must  be  maintained  for  a  sufficient  time  at  a 
temperature  of  incandescence.  These  conditions  are  simple,  but  the 
necessity  of  providing  them  is  not  always  kept  in  view.  ...  It 
would  be  unsuitable  here  to  mention  the  names  of  the  numerous 
makers  of  these  appliances,  but  it  may  with  confidence  be  asserted  that 
consumers  of  coal  in  almost  all  kinds  of  furnaces  have  it  now  in  their 
power  to  conform  with  the  requirements  of  the  Public  Health  Act, 
and  prevent  the  discharge  of  black  smoke  from  their  chimneys.  As  a 
proof  of  this,  one  prominent  instance  can  be  mentioned  of  a  large  chem- 
ical works,  where  may  be  seen  a  row  of  50  large  Lancashire  boilers, 
each  with  two  furnaces,  and  an  equal  number  of  furnaces  applied  to 
other  purposes  than  that  of  raising  steam,  making  in  all  as  many  as 
200  fires.  Till  lately  a  row  of  four  chimneys  poured  out  a  mass  of 


158  STEAM-BOILER  ECONOMY. 

black  smoke,  which  shrouded  the  whole  district  in  its  pall;  now  they 
are  smokeless  as  far  as  color  is  concerned,  and  only  fully  burnt  color- 
less gases  are  sent  into  the  air. ' ' 

Requirements  of  a  Smoke-preventing  Furnace. — A  committee  ap- 
pointed by  the  Engineers'  Club  of  St.  Louis  in  1891  investigated  the 
various  smoke-consuming  devices  then  in  the  market.  After  defining 
the  nature  of  the  problem  of  smoke-consumption  the  committee  laid 
'down  the  following  ten  requirements  which  any  smoke-consuming  or 
preventing  device  must  satisfy  in  order  to  fully  meet  the  varying  con- 
ditions obtaining  in  ordinary  practice,  viz. : 

1.  It  should  develop  such  high  temperature  and  oxidizing  action 
as  to  insure  the  combustion  of  the  free  or  separate  carbon  which  forms 
the  visible  smoke. 

2.  It  should  insure  regularity  of  action  under  the  varying  condi- 
tions induced  by  charging  fresh  coal,  cleaning  fires,  inattention  of  fire- 
man, etc. 

3.  It  should  not  be  susceptible  to  derangement  under  the  conditions 
likely  to  obtain  in  use,  such  as  carelessness  of  firemen,  inferior  water, 
bad  clinker,  etc. 

4.  If  there  is  any  increase  in  the  cost  of  operation  it  should  be 
•small. 

5.  The   capacity  of  the  apparatus  should  be  such  that  efficient 
action  will  be  secured  not  only  when  the  boiler  is  working  up  to  its 
full  rated  capacity,  but  even  when  forced  in  order  to  meet  extraordi- 
nary demands. 

6.  The  apparatus  should  be  readily  adjustable  to  all  forms  of  boilers 
and  boiler-settings. 

7.  It  should  be  susceptible  of  application  to  boiler-settings  where 
the  space  is  already  limited. 

8.  It  should  be  of  comparatively  low  first  cost.  * 

9.  Repairs  should  be  small  in  amount,  easily  made  and  low  of  cost. 

10.  The  apparatus  should  operate  without  injury  to  boiler  or  other 
accessories. 

The  committee  classified  the  various  types  of  smoke-preventing  de- 
vices which  have  thus  far  been  proposed,  as  follows : 

1.  Steam- jets. 

2.  Fire-brick  arches  or  checker- work. 

3.  Hollow  walls  for  preheating  air. 

4.  Coking-arches  or  chambers. 

5.  Double-combustion  furnaces. 

6.  Downward-draught  furnaces. 

7.  Automatic  stokers. 

*  This  is  not  evident.  With  Illinois  coals  a  saving  of  from  10  to  20  per  cent 
may  be  made  by  the  use  of  a  good  smoke-preventing  furnace  as  compared  with 
the  ordinary  furnace.  This  would  warrant  the  use  of  the  most  costly  furnace  or 
automatic  stoker  in  the  market. 


FURNACES.— METHODS  OF  FIRING,  ETC.  159 

Methods  of  Securing  Complete  Combustion. — The  fundamental 
condition  of  perfect  combustion  of  soft  coal  is  that  every  particle  of 
the  gas  distilled  from  the  coal,  including  the  water-gas  made  by  de- 
composing its  moisture,  be  brought  in  contact  with  a  sufficient  supply 
of  very  hot  air  to  burn  it,  the  mixing  of  the  gas  and  air  taking  place 
at  a  sufficient  distance  from  the  heating  surfaces  of  the  boiler  so  that 
they  do  not  become  cooled  below  the  temperature  of  ignition  before  the 
combustion  takes  place.  It  is  impossible  to  secure  this  condition  in  an 
ordinary  furnace  with  hand-firing  and  a  level  bed  of  coal. 

It  may  be  secured,  however,  to  a  considerable  extent  with  hand-fir- 
ing if  some  modifications  of  the  furnace  and  of  the  method  of  firing 
are  made.  The  change  required  in  the  furnace  is  the  roofing  of  it 
with  fire-brick  and  the  provision  of  a  large  fire-brick  combustion-cham- 
ber in  which  there  shall  be  sufficient  space  and  time  allowed  for  the 
separate  currents  of  gas  and  of  heated  air  to  become  intimately  mixed 
before  coming  in  contact  with  the  boiler  surfaces. 

The  Coking  System  of  Firing. — The  change  required  in  the  method 
of  firing  is  such  a  change  that  the  whole  bed  of  the  fire  shall  not  at  the 
same  time  be  covered  with  fresh  fire.  To  effect  this,  either  the  coking 
system  or  the  alternate-firing  system  may  be  used.  In  the  first,  or 
coking  system,  the  fresh  coal  is  piled  up  on  the  front  half  of  the  bed 
while  the  rear  half  has  a  level  bed  of  half-burned  coal  upon  it.  The 
gases  distilled  from  the  fresh  coal  then  pass  over  the  rear  half,  through 
which  an  excess  of  air  is  entering,  being  heated  as  they  pass  through 
the  bed  of  coke.  The  two  currents  of  gas,  one  containing  the  distilled 
gases  and  the  other  the  supply  of  hot  air.  intermingle  in  the  hot  com- 
bustion-chamber. When  nearly  all  of  the  gas  has  been  distilled  from 
the  pile  of  coal  in  the  front  half  of  the  furnace,  the  pile  is  pushed  back 
and  levelled  over  the  rear  half,  and  either  immediately  or  within  a 
minute  or  two,  according  to  whether  the  gases  have  been  more  or  less 
completely  driven  off,  fresh  coal  is  again  piled  in  front.  With  some 
coals  the  coking  system  cannot  be  advantageously  used,  namely,  those 
coals  which  contain  a  large  quantity  of  very  fusible  ash.  In  pushing 
back  the  coked  coal  onto  the  rear  of  the  grates,  the  ash  lying  thereon, 
and  which  may  have  been  kept  below  the  fusing  temperature  by  the 
air  passing  through  it,  becomes  mixed  with  the  coked  coal,  which  just 
after  being  pushed  back  burns  with  great  rapidity,  generating  a  very 
high  temperature,  melting  the  ash  and  causing  it  to  run  and  choke 
the  air-spaces  in  the  grate. 

The  coking  system  involves  a  greater  amount  of  labor  and  attention 


160 


STEAM-BOILER  ECONOMY. 


on  the  part  of  the  firemen  than  ordinary  level  firing,  and  they  some- 
times object  to  it  on  that  account.  To  what  extent  the  coking  system 
of  firing  will  reduce  the  amount  of  smoke  depends  on  the  character  of 
the  coal,  on  the  skill  of  the  fireman,  and  on  the  size  of  the  fire-brick 
combustion-chamber.  The  lower  the  percentage  of  moisture  and  vola- 
tile matter  the  less  smoke  will  be  made  with  any  system  of  firing,  and 
the  more  complete  will  be  its  suppression  with  the  coking  system. 
The  smaller  the  quantity  of  fresh  coal  fired  at  a  time,  and  the  greater 
the  care  exercised  by  the  fireman  to  keep  the  quantities  fired  each  time 
and  the  intervals  between  firing  uniform,  and  to  keep  the  bed  of  coal 
in  the  rear  level  and  not  too  thick,  the  less  will  be  the  amount  of 
smoke.  The  larger  the  combustion-chamber  in  which  the  currents  of 
smoky  gas  and  of  hot  gas  surcharged  with  air  unite,  the  longer  time 
will  be  afforded  for  their  admixture,  the  more  complete  will  be  the 
combustion,  and  the  less  will  be  the  smoke. 

The  Walker  Furnace,  Fig.  17,  represents  a  furnace  in  which  the 
coking  system  of  firing  is  used.  The  forward  part  of  the  grate,  F, 
is  stationary,  and  slopes  towards  the  rear  of  the  furnace.  Back  of  it 
is  a  dumping-grate,  D.  The  fresh  fuel  is  fired  upon  the  front  part  of 
the  grate,  and  after  the  volatile  gases  have  been  distilled  it  is  pushed 
back  upon  the  dumping-grate.  Air  is  admitted  through  both  grates, 
and  also  through  the  conduit,  K.  The  air  for  this  conduit  may  be 


Longitudinal   Section.  Cross  Section  M-N. 

FIG.  17. — THE  WALKER  FURNACE. 

brought  from  passages  in  the  side  walls  in  which  it  is  heated.  A  fire- 
brick arch,  C,  with  a  vertical  wall,  B,  above  it,  serves  to  deflect  the 
mixture  of  air  and  smoky  gases  down  upon  the  incandescent  coke 
lying  upon  the  dumping-grate.  This  insures  complete  and  smokeless 
combustion  if  proper  care  is  used  in  firing. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


161 


Alternate  Firing. — A  method  of  firing  which  seems  to  have  all  the 
advantages  of  the  coking  system,  and  none  of  its  disadvantages,  is  that 
known  as  alternate  firing.  It  consists  in  firing  fresh  coal,  first  on  one 
half  of  the  bed  of  the  furnace,  and  then  on  the  other  half,  alternately, 
at  equal  intervals  of  time.  Instead  of  covering  the  whole  bed  with 
fresh  coal,  say  every  ten  minutes,  only  half  the  bed  is  covered  at  each 
firing,  and  the  other  half  is  covered  five  minutes  afterwards.  After 


FIG.  18. — THE  "WING-WALL"  FURNACE  APPLIED  TO  A  WATER-TUBE  BOILER. 

each  addition  of  fresh  coal  the  volatile  gases  that  arise  from  it  come  in 
contact  with  the  current  of  hot  gas,  carrying  an  excess  of  air,  which 
arises  from  the  half-burned  coal  on  the  other  half  of  the  bed.  In  this 
system  of  firing  the  fresh  coal  may  be  fired  alternately,  either  in  the 
front  and  rear  of  the  bed,  or  on  the  right  and  left  side,  the  former 
being  called  alternate  front  and  back  firing,  and  the  latter  alternate 
side  firing.  With  this  system  of  firing  the  successful  prevention  of 
smoke  depends  largely  on  the  skill  of  the  fireman,  but  more  especially 


162  STEAM-BOILER  ECONOMY. 

on  the  size  of  the  combustion-chamber,  and  the  opportunity  it  affords 
for  thorough  admixture  of  the  two  currents  of  gas.  Baffle-walls  placed 
in  the  combustion-chambers  to  compel  the  gases  to  take  a  circuitous 
direction  facilitate  the  mixture,  and  together  with  the  side  walla  and 
fire-brick  roof,  have  what  is  called  a  regenerative  action,  on  the  prin- 
ciple of  the  Siemens  regenerators,  used  in  steel-melting  furnaces, 
absorbing  heat  during  the  times  when  the  burning  gases  are  the  hot- 
test, and  giving  out  heat  to  the  gases  when  they  are  cooler,  or  imme- 
diately after  the  firing  of  fresh  coal. 

Alternate  firing  is  of  no  use  unless  there  is  a  large  combustion- 
chamber  in  which  the  two  gaseous  currents  are  mixed  and  the  smoke 
burned  before  they  are  allowed  to  come  in  contact  with  the  heating 
surface. 

The  "Wing-wall"  Furnace. — This  furnace  was  patented  by  the 
author  May  17,  1898.  It  is  adapted  for  the  smokeless  combustion  of 
soft  coal,  peat,  wood,  tan-bark,  and  other  fuels  that  contain  large  pro- 
portions of  volatile  matter  and  moisture. 

The  drawings,  Fig.  18,  show  the  furnace  applied  to  a  water-tube 
boiler.  C  is  a  fire-chamber  or  oven,  built  of  brick  and  extending  out 
in  front  of  the  boiler.  In  it  the  fuel  is  burned,  either  on  the  ordinary 
grate-bars  or  by  means  of  a  mechanical  stoker.  D  is  an  ordinary 
bridge  wall.  EE'  are  two  tall  vertical  walls  called  wing- walls,  built 
some  distance  in  the  rear  of  the  bridge  wall.  G  is  a  combustion - 
chamber.  HH  are  several  piers  of  fire-brick,  projecting  into  the 
chamber  G,  from  the  rear  wall  J.  K  is  the  ordinary  partition  wall 
built  across  the  boiler-tubes,  and  M  is  a  tile  roof  to  the  chamber  F  to 
prevent  the  gases  in  that  chamber  from  reaching  the  tubes  until  after 
they  have  passed  through  the  narrow  vertical  passage  between  the 
wing- walls  EE'. 

In  operation  with  hand-firing,  the  alternate  method  of  firing  is 
used.  The  fresh  coal  is  spread  alternately  on  the  right  and  left  sides 
of  the  grate  at  equal  intervals  of  time.  Immediately  after  firing  on 
one  side  dense,  smoky  gases  arise  on  that  side,  while  on  the  other  side 
an  excessive  supply  of  very  hot  air  is  passing  through  the  bed  of  par- 
tially burned  coal  or  coke.  These  two  currents,  one  of  cool,  smoky 
gas  and  the  other  of  clear,  hot  gas  with  a  large  excess  of  air,  pass  side 
by  side  over  the  bridge  wall  D,  but  they  are  compelled  to  change  their 
direction  and  mingle  together  on  passing  through  the  tall,  narrow  pas- 
sage between  the  wing- walls  EE',  and  by  so  mingling,  the  gases  are 
burned  and  smoke  is  prevented. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


163 


The  combustion  is  assisted  by  the  heat  radiated  from  the  walls  of 
the  combustion-chamber  G  and  the  piers  If,  which  absorb  heat  dur- 
ing the  time  when  the  fire  is  hottest — that  is,  just  before  fresh  coal  is 
spread  on  the  grate,  and  give  out  heat  to  the  gases  in  the  chamber  G 
when  the  fire  is  coolest — that  is,  just  after  firing,  when  the  smoky 
gases  are  escaping.  They  act  on  the  principle  of  the  Siemens  regen- 
erative furnace,  commonly  used  in  steel-works. 


Sectional  Plan  a-b. 

PIG  19. — THE  " WING- WALL"  FURNACE  APPIED   TO  A  HORIZONTAL  TUBULAB 

BOILER. 

Fig.  1 9  shows  a  modification,  of  the  furnace  applied  to  a  horizontal 
tubular  boiler  (patented  Feb.  ,  1901).  In  this  arrangement  the  oven 
built  in  front  of  the  boiler  is  dispensed  with,  and  the  space  in  the 
rear  of  the  bridge  wall  is  used  for  a  combustion-chamber.  GG  here 
are  the  wing-walls,  and  //  an  intercepting  wall,  built  so  as  to  prevent 
the  gases  passing  over  the  arch. 

Introduction  of  Heated  Air  into  the  Furnace. — The  admission  of 
heated  air  into  the  furnace,  through  hollow  bridge  and  side  walls  or 
through  channels  in  fire-brick  arches  over  the  furnace,  has  long  been 
a  favorite  method  of  inventors  of  appliances  for  producing  smokeless 
combustion,  and  numerous  patents  have  been  taken  out  for  such  appli- 
ances during  the  last  fifty  years  or  more.  The  theory  of  this  method 
of  improving  combustion  is  correct,  but  it  has  usually  failed  to  come 


164  STEAM-BOILER  ECONOMY. 

into  extensive  use  on  account  of  practical  difficulties.  The  usual 
troubles  are  that. the  air  is  not  made  hot  enough,  that  not  enough  air  is 
introduced  into  the  furnace  at  the  time  when  it  is  needed,  that  is,  just 
after  fresh  coal  has  been  fired,  and  too  much  is  admitted  when  little  or 
none  is  needed,  or  when  sufficient  air  is  passing  through  the  grates. 
The  air-passages  also  are  apt  to  become  clogged  with  dust.  Sometimes 
air  is  forced  into  the  passages  by  means  of  a  steam- jet,  and  some  benefit 
in  diminishing  smoke  is  apparent,  but  a  loss  of  economy  usually  results, 
and  the  use  of  the  jet  is  abandoned.  Automatic  appliances  for  ad- 
mitting air  just  after  firing,  and  shutting  it  off  gradually  during  two  or 
three  minutes  following,  have  also  been  used  sometimes  with  apparently 
good  results,  but  they  do  not  appear  to  have  been  generally  successful. 
Admitting  cold  air  above  the  coal  will  be  of  no  use  to  burn  these  gases 
unless  it  becomes  highly  heated  after  its  admission  by  contact  with  or 
radiation  from  the  hot  walls  of  the  furnace  and  combustion-chamber. 
When  there  is  a  long  fire-brick  combustion-chamber  in  the  rear  of  the 
furnace  in  which  the  air  and  gases  may  unite,  the  automatic  admission 
of  air  just  after  firing,  and  its  gradual  shutting  off  may  prove  benefi- 
cial both  in  diminishing  smoke  and  in  improving  economy. 

Jets  of  steam  are  sometimes  blown  into  the  furnace,  above  the  fire, 
carrying  jets  of  air  with  them,  on  the  principle  of  the  injector.  That 
they  do  decrease  the  amount  of  smoke  in  some  cases  there  seems  to 
be  no  doubt.  Eeasons  which  have  been  given  to  explain  the  action  of 
the  jet  and  which  may  to  some  extent  be  true  are  the  following : 

(1)  The  diminution  of  smoke  is  apparent  and  not  real.     Both  the 
air  and  the  steam  .dilute  the  smoke,  and  make  it  less  dense  in  appear- 
ance as  it  escapes  from  the  top  of  the  chimney.     The  steam  also  escap- 
ing from  the  chimney  as  a  white  cloud  disguises  the  smoke  and  may 
condense  its  bulk,  rendering  it  less  visible.     Further,  the  chilling  action 
of  the  air  and  steam  may  decrease  the  rapidity  of  production  of  the 
smoke  in  the  furnace,  extending  its  production  over  a  longer  period  of 
time,  decreasing  its  density  during  that  time. 

(2)  The  jet  of  air  violently  driven  in  by  the  steam  and  pointed 
downwards  onto  the  bed  of  coal,  becomes  intimately  mixed  with  the 
gases  distilled  from  the  coal,  and  then  if  there  is  a  long  run  through 
the  hot  combustion-chamber  the  mixture  will  be  burned,  destroying 
the  smoke. 

The  steam-jet  is  in  itself  a  wasteful  appliance,  for  even  if  the  steam 
is  decomposed  and  the  gases  afterwards  completely  burned,  forming 
steam  again,  it  escapes  from  the  boiler  superheated  to  the  temperature 


FURNACES.— METHODS  OF  FIRING,  ETC. 


165 


of  the  flue  gases,  which  temperature  is  always  higher  than  that  of  the 
steam  in  the  jet,  and  there  is  a  consequent  loss  of  heat  due  to  the  sup- 
erheating. 

Downward  Draft  Furnaces. — In  ordinary  hand-fired  furnaces,  fresh 
coal  is  fed  on  top  of  the  bed,  and  the  air  passes  upwards  through  the 
grate,  then  through  the  very  hot  partially  burned  coal  or  coke  lying  on 
the  grate,  and  finally  through  the  fresh  coal  from  which  the  volatile 
gases  are  being  distilled.  If  the  direction  of  the  draft  can  be  reversed, 
the  air  being  admitted  above  the  coal  and  passing  down  through  it  and 
through  the  grate,  the  character  of  the  operation  of  the  furnace  is 
completely  changed.  The  cold  air  and  the  cool  distilled  gases  pass  to- 
gether down  through  the  hot  coke,  and  if  the  air-supply  is  sufficient 
the  gases  will  be  thoroughly  burned  and  smoke  will  be  prevented.  To 
prevent  the  burning  out  of  the  grate-bars  they  are  made  of  water-tubes, 
which  are  connected  by  headers  with  the  boiler  so  as  to  insure  a  positive 
circulation  of  the  water  through  them. 

The  Hawley  Down-draft  Furance. — This  is  a  form  of  down- 
draft  furnace  which  has  within  the  past  few  years  been  widely  intro- 


FIGL  20.— HAWLEY  DOWN-DRAFT  FURNACE  APPLIED  TO  A  HEINE  BOILER. 

duced  in  the  United  States,  and  has  given  excellent  results  both  in 
smoke-prevention  and  in  economy  of  fuel.     Besides  the  water-grate 


166  STEAM-BOILER  ECONOMY. 

upon  which  the  coal  is  fed,  there  is  a  lower  or  common  grate,  upon 
which  is  burned  the  coke  that  falls  through  the  water-grate.  The 
greater  part  of  the  air-supply  is  admitted  above  the  fresh  coal  on  the 


Era.  21. — WATER-GRATE  USED  IN  THE  HAWLEY  FURNACE. 

water-grate,  passing  through  the  coal,  and  an  additional  supply  is 
admitted  below  the  lower  grate,  passing  upwards  through  it  to  burn 
the  coke  and  to  assist  in  burning  the  gases.  The  space  between  the 
two  grates  forms  part  of  the  combustion-chamber  in  which  the  gases 
are  burned. 

Fig.  20  shows  a  Hawley  furnace  as  applied  to  a  Heine  water-tube 
boiler  and  Fig.  21  a  view  of  the  water-grate.  The  pipe-connections  by 
which  a  circulation  £>f  water  is  insured  through  the  water-grate  are 
also  shown  in  Fig.  20. 

Automatic  or  Mechanical  Stokers. — More  than  fifty  years  ago 
mechanical  stokers  fcr  feeding  coal  regularly  by  machinery  were  suc- 
cessfully used  in  England,  although  their  use  has  not  even  there  become 
by  any  means  universal.  Within  the  last  ten  years  they  have  become 
quite  common  in  the  United  States,  especially  in  large  and  modern 
boiler  plants.  By  the  use  of  such  stokers  the  chief  objections  to 
hand-firing  are  avoided,  viz.,  the  intermittent  supply  of  coal,  the 
sudden  volatilization  of  great  volumes  of  smoky  gas,  the  alternately 
deficient  and  excessive  air-supply,  and  the  cooling  due  to  frequent 
opening  of  the  fire-door.  When  properly  designed  and  operated 
these  stokers  feed  both  the  coal  and  the  air  at  a  regular  rate,  and 
when  the  air  and  the  coal-supply  are  properly  adjusted  to  each 
other,  and  proper  provisions,  such  as  a  fire-brick  combustion-chamber 
or  other  means,  are  made  for  compelling  the  currents  of  gas  and 
air  to  become  completely  intermingled,  they  will  burn  coal  with- 


FURNACES.— METHODS  OF  FIRING,  ETC.  167 

out  smoke  and  at  the  same  time  with  the  maximum  economy  which 
the  design  and  proportions  of  the  boiler  permit.  Moreover,  in  large 
plants  they  are  capable  of  effecting  a  great  saving  of  labor,  especially 
when  they  are  used  in  conjunction  with  modern  methods  of  storing  coal 
in  overhead  bins  and  feeding  it  by  gravity  through  chutes  into  the 
hoppers  of  the  stoker.  The  chief  objection  to  them  is  their  initial 
first  cost.  In  large  well-designed  plants,  however,  this  objection  is  to 
a  great  extent,  if  not  entirely,  overcome  by  the  fact  that  when  the 
stokers  and  their  rate  of  driving  are  properly  proportioned  to  the 
boilers,  it  is  possible  to  obtain  from  a  boiler  considerable  increase  of 
capacity  compared  with  hand-firing,  without  any  sacrifice  of  economy, 
and  therefore  the  number  of  boilers  required  may  be  less  than  with 
hand-firing. 

The  introduction  of  mechanical  stokers  in  the  United  States  hav- 
ing been  so  comparatively  recent,  and  the  correct  methods  of  propor- 
tioning and  handling  them  having  been  not  in  all  cases  well  under- 
stood, it  is  not  to  be  expected  that  there  will  already  be  a  general 
consensus  of  opinion  in  their  favor.  As  evidence  of  the  difference  of 
opinion  concerning  them,  the  following  extracts  from  a  report  made  by 
Mr.  E.  S.  Hale,  of  Boston,  Mass.,  to  the  Steam  Users'  Association 
(which  association  had  the  short  life  of  one  year)  in  January,  1897, 
may  be  of  interest : 

To  the  circular  requesting  information  on  mechanical  stokers  we 
received  in  all  twelve  replies. 

These  covered  the  Wilkinson,  Murphy,  Brightman,  Hodgkinson, 
American,  Babcock  &  Wilcox,  Eoney,  and  Meissner  types,  and  the 
twelve  plants  covered  sixteen  experiences. 

In  reply  to  the  question,'"  Do  stokers  save  coal  overhand-firing?" 
one  reply  showed  a  loss  in  economy,  five  reported  no  saving,  and  six 
reported  a  saving.  The  balance  could  not  tell.  One  plant  reports  a 
large  saving  due  to  using  a  cheaper  grade  of  coal  than  could  be  fired 
by  hand. 

In  reply  to  the  question,  "  Do  stokers  save  labor  over  hand-firing  ?  " 
one  found  increased  cost  in  labor,  three  found  no  saving,  and  eight 
found  a  saving.  Three  of  the  four  who  found  a  loss  or  found  no  sav- 
ing in  labor  thought  that  if  they  should  fully  equip  their  plants  with 
stokers  they  could  arrange  to  save  labor. 

In  reply  to  the  question,  "Do  stokers  save  smoke  over  hand-fir- 
ing?" two  soft-coal  plants  thought  they  did  not  save  smoke,  seven 
thought  they  did.  The  others  used  hard  coal  or  did  not  reply. 

No  plant  replied  to  the  question  as  to  whether  the  stoker  caused  a 
net  saving. 

As  to  repairs,  only  five  had  had  stokers  in  use  over  two  years,  and 


168  STEAM-BOILER  ECONOMY. 

of  these  three  replied  that  the  repairs  were  "  small  "  or  "  trifling  " ; 
the  other  two  did  not  reply  to  the  question  on  repairs. 

In  reply  to  the  question,  ' (  Do  stokers  respond  to  a  sudden  call  for 
steam  as  well,  better,  or  worse  than  hand-firing?  "  five  thought  they 
responded  slower,  one  as  quickly  as,  and  five  quicker  than  hand-firing. 

In  reply  to  the  question  "as  to  draft  needed,"  three  thought  they 
needed  more  draft,  four  thought  they  needed  the  same,  and  one  less 
draft  than  hand  firing. 

After  trials,  in  five  cases  the  plants  did  not  intend  to  increase  the 
number  of  stokers  or  had  already  discarded  them.  Three  plants  were 
doubtful,  while  six  intended  to  increase  the  stoker-plant  either  at  once 
or  when  they  put  in  new  boilers. 

The  answers  to  these  questions  may  not  appear  to  be  very  favorable 
to  mechanical  stokers,  but  there  are  many  possible  reasons  for  the  un- 
favorable replies,  other  than  the  inefficiency  of  the  stokers.  It  is  prob- 
able that  most  of  the  replies  were  received  from  parties  who  are  using 
the  stokers  with  semi-bituminous  and  not  with  bituminous  coal,  and 
with  the  former  there  is  not  the  same  margin  for  saving  that  there  is 
with  the  latter.  In  other  cases  the  stokers  may  have  been  handled 
unskillfully  or  may  not  have  been  properly  proportioned  to  the  boiler. 

It  is  probable  also  that  if  a  more  extensive  census  were  taken  now 
of  the  opinions  of  users  of  stokers,  the  results  would  be  much  more 
favorable,  for  during  the  last  few  years  the  manufacturers  of  stokers 
have  done  a  large  business,  introducing  them  in  many  cases  in  plants 
of  several  thousand  horse-power. 

Types  of  Mechanical  Stokers. — The  stokers  now  in  common  use 
may  be  divided  into  four  general  classes,  depending  on  the  kind  of 
mechanism  used  for  feeding  the  coal.  In  the  first  class  the  coal  is 
carried  on  grate-bars,  either  horizontal  or  inclined  more  or  less,  the 
individual  bars,  or  sometimes  alternate  bars,  being  given  a  reciprocat- 
ing to  and  fro,  up  and  down,  or  rocking  motion,  by  which  the  coal  is 
gradually  advanced  along  the  grates.  In  the  second  class  the  grate  is 
steeply  inclined,  and  the  coal  is  pushed  onto  its  upper  end,  and  slides 
down  slowly  as  it  burns.  In  the  third  class  the  whole  grate  forms  an 
endless  chain  of  short  bars,  on  which  the  coal  travels  horizontally  into 
the  furnace,  the  chain  passing  over  a  sprocket-wheel  at  the  end  and 
returning  through  the  ash-pit.  In  the  fourth  class  the  fresh  coal  is  fed 
in  underneath  the  burning  coal,  and  the  gases  distilled  from  it  pass 
through  the  bed  of  hot  coke  above,  the  action  being  exactly  the  reverse 
of  that  of  the  Hawley  down-draft  furnace,  in  which  the  fresh  coal  is 
fed  on  top  of  the  bed,  and  the  gases  pass  down  through  the  bed  of  hot 


FURNACES.— METHODS  OF  FIRING,  ETC. 


169 


coke  beneath.     A  brief  description  of  some  modern  forms  of  stokers 
will  now  be  given. 

The  Vicars  Mechanical  Stoker  (Fig.  22). — The  fuel  is  fed  from  a 
hopper  into  two  cases  or  boxes,  from  which  it  is  gradually  pushed 
by  reciprocating  plungers  onto  a  coking  plate,  where  it  lies  in  a 
mass  about  12  ins.  deep,  and  where  its  volatile  gases  are  evolved. 


FIG.  22. — THE  VICARS  MECHANICAL  STOKER. 

Thence  it  passes  onto  the  grate-bars,  which  by  a  slow  reciprocating 
movement  carry  the  burning  mass  gradually  backward.  Such  uncon- 
sumed  coal  as  reaches  the  end  of  the  grate-bars,  together  with  the 
clinker  and  ash-refuse  carried  back,  are  discharged  over  the  ends  of 
the  fire-bars  onto  a  stationary  grate  at  a  lower  level. 

The  two  separate  mechanical  movements  in  the  operation  of  this 
stoker,  each  independent  of  the  other,  are  driven  by  auxiliary  power. 
The  coal-feed  is  varied  by  altering  the  rate  of  motion  of  the  plungers, 
which  by  the  movement  of  a  lever  can  be  adjusted  to  a  movement  from 
slow  to  rapid  as  the  consumption  of  fuel  may  require.  The  recipro- 
cating action  of  the  grate-bars  is  operated  in  the  same  way  as  the  coal- 
feed,  but  with  several  intermediate  variations  from  a  state  of  rest  to  a 


170 


STEAM-BOILER  ECONOMY. 


movement  of  3J  ins.  The  bars  of  each  furnace  are  arranged  in  two 
sets,  each  composed  of  the  alternate  bars,  which  sets  operate  together 
in  moving  inward,  but  return  at  separate  intervals.  Thus  the  fuel  is 
carried  inward  by  the  simultaneous  action  of  both  sets  of  bars,  and 
remains  in  place,  without  being  disturbed  by  the  return  of  either  set. 
Each  successive  inward  movement  of  the  bars  serves  to  carry  the  fuel, 
together  with  the  clinker  and  ash-refuse,  nearer  to  the  inner  end  of  the 
grate,  where  the  mass  at  length  drops  over  into  the  combustion-chamber, 
and  forms  and  maintains  a  bank  which  acts  as  a  bridge  and  on  which 
the  combustion  of  the  unconsumed  fuel  is  in  due  time  completed. 

The  Coxe  Automatic  Stoker  *  (Fig.  23)  is  of  the  chain-grate  variety. 
It  was  designed  for  burning  small  sizes  of  anthracite,  but  has  also  been 
found  adapted  to  bituminous  coal.  Its  peculiar  feature  is  the  means 


\  ^fess 


FIG.  23. — THE  COXE  AUTOMATIC  STOKER. 

used  to  graduate  the  air-supply  to  the  requirements  of  different  por- 
tions of  the  travelling  bed  of  coal.  Under  the  horizontal  travelling 
grate  are  placed  a  number  of  air-chambers  or  boxes,  made  of  sheet  iron, 
open  at  the  top,  and  provided  with  dampers  in  the  partitions  between 
them.  Blast  from  a  fan  is  delivered  into  the  larger  chamber  B  in  the 
diagram,  and  part  of  it  passes  into  the  other  chambers  at  reduced 
pressures.  The  air  passes  from  these  chambers  through  the  grates  at 
pressures  which  may  be  regulated  by  the  dampers.  The  coal  descend- 
ing from  the  hopper  over  the  highly  heated  sloping  surface  of  fire- 
brick is  ignited  as  it  reaches  the  first  section  of  the  travelling  grate. 

*A  detailed  description  of  tins  stoker  is  given  in  a  paper  by  Eckley  B.  Coxe,  in 
Trans.  Am.  Inst.  Mining  Engineers,  vol.  xxii.  1893. 


FURNACES.— METHODS  OF  FIRING,  ETC.  171 

As  it  passes  over  the  first  chamber,  A,  it  receives  a  blast  of  moderate 
pressure,  then  a  higher  pressure  from  B,  then  diminished  pressures  from 
C  and  D  as  the  bed  of  coal  becomes  thinner.  The  object  is  to  subject 
the  coal  as  soon  as  it  arrives  on  the  grate  to  a  pressure  of  blast  which 
is  the  proper  one  to  ignite  it,  then  to  burn  it  with  a  blast  as  strong  as 
will  produce  good  combustion,  and  as  the  carbon  is  eliminated  and  the 
thickness  of  the  bed  becomes  smaller  to  diminish  the  blast  to  corre- 
spond with  these  conditions.  The  mass  of  coal  remains  all  the  time 
in  practically  the  same  position  and  condition  in  which  it  was  placed 
on  the  grate,  except  so  far  as  altered  by  the  combustion.  The  ashes 
are  carried  off  or  dumped  by  the  grate-bars  as  they  descend. 

The  coal  burns  out  from  the  bottom ;  that  is,  the  first  thin  layer 
of  complete  ash  forms  on  the  bottom  and  gradually  becomes  thicker 
until  it  reaches  to  the  top.  At  first  the  ash  is  very  hot,  but  the  gentle 
current  of  air  passing  through  it  gradually  cools  it  off,  and  when  it  is 
dumped  into  the  ash-pit  it  is  not  very  hot.  The  shaded  portion  begin- 
ning in  C  and  extending  into  D  represents  the  gradual  formation  of 
the  ash,  and  the  part  to  the  left  of  that  shows  the  ash  practically  cooled 
or  cooling. 

A  certain  portion  of  air  from  which  the  oxygen  is  not  removed 
passes  through  and  cools  the  ash,  but  in  the  first  sections  of  the  bed  of 
fuel  near  A  a  certain  amount  of  carbonic  oxide  is  formed,  due  to  the 
fact  that  the  amount  of  air  blown  through  is  not  sufficient  to  properly 
consume  all  the  carbon.  This  carbonic  oxide  is  burned  in  the  furnace 
by  the  air  which  has  passed  through  the  ash. 

The  results  of  some  tests  of  the  Coxe  stoker  with  pea  and  buck- 
wheat coal  will  be  found  in  the  chapter  on  "  Results  of  Boiler  Trials. " 

The  Playford  Stoker,  Fig.  24,  is  another  chain-grate  stoker.  To- 
the  traveling-chains  are  attached  a  series  of  wrought-iron  T  bars,  run- 
ning across  the  furnace,  and  these  carry  the  small  cast-iron  sections  of 
which  the  grate  is  made.  Below  the  chain-grate  a  screw- conveyor  is 
placed  for  carrying  the  ashes  forward  from  the  rear  of  the  furnace  to 
the  ash-pit  in  front. 

The  Babcock  &  Wilcox  Stoker,  Fig.  25,  is  also  an  endless-chain 
grate.  It  has  been  used  with  much  success  in  the  West  with  bitu- 
minous coals.  The  cut  shows  the  stoker  removed  from  the  furnace. 
The  large  vertical  pipe  is  the  coal-feeder,  which  delivers  coal  from  an 
overhead  bin  into  the  hopper.  It  is  driven  by  a  worm-wheel,  the 
power  being  delivered  to  the  worm  from  an  independent  engine 
through  a  lever  and  ratchet-wheel. 


172 


STEAM-BOILER  ECONOMY, 


Longitudinal   Section, 
FIG.  24. — THE  PLATFORD  STOKER. 


FIG.  25. — THE  BABCOCK  &  Wu.cox  STOKER. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


173 


The  Eoney  Mechanical  Stoker — This  stoker  was  first  brought  out 
in  1885.     The  present  construction  is  shown  in  Fig.  26.     It  receives 


FIG.  26. — THE  ROONEY  MECHANIC  AT,  STOKER. 

the  fuel -in  bulk,  and,  without  further  handling,  feeds  it  continuously 
and  at  any  desired  rate  to  the  furnace,  burns  the  combustible  portion 
and  deposits  the  ash  and  cinder  in  the  ash-pit  ready  for  removal. 

.  In  the  bottom  of  the  coal -hopper  is  located  a  sliding  pusher,  which 
gradually  feeds  the  coal  over  the  dead-plate  and  on  to  the  grate.  The 
latter  consists  of  horizontal  flat-surfaced  overlapping  bars,  extending 
from  side  to  side  of  the  furnace,  and  inclined  at  an  angle  of  37  de- 
grees from  the  horizontal.  In  the  wider  furnaces  two  or  more  sets  of 
grate-bars  are  placed  side  by  side,  provided  with  independent  actuating 
connections.  The  grate-bars  rock  in  unison,  assuming  alternately  a 
stepped  and  an  inclined  position.  When  they  rock  forward  into  the 
inclined  position  the  burning  coal  tends  to  work  down  in  a  body,  but 
before  it  can  move  too  far  the  bars  rock  back  to  the  stepped  position, 
checking  the  downward  motion,  breaking  up  the  bed  of  fuel  and  freely 


174  STEAM-BOILER  ECONOMY. 

admitting  air  through  the  fire.  This  alternate  starting  and  checking 
motion  keeps  the  fire  constantly  stirred  and  opened  up  from  beneath, 
and  finally  lands  the  cinder  and  ash  on  the  dumping-grate,  from  which 
it  is  discharged  into  the  ash-pit.  The  depending  webs  of  the  grate- 
bars  are  perforated  with  longitudinal  slots,  so  placed  that  the  condi- 
tion of  the  fire  can  be  seen  at  all  times  and  free  access  had  to  all  parts 
of  the  grate  without  the  opening  of  doors.  These  slots  also  serve  to 
furnish  an  abundant  supply  of  air  for  combustion.  The  motion  of  the 
grate-bars  and  the  feeding  device  is  regulated  by  two  simple  adjust- 
ments, by  which  the  action  of  the  stoker  is  controlled  and  the  fires 
are  forced,  checked  or  banked  at  will. 

A  coking-arch  of  fire-brick  is  sprung  across  the  furnace,  covering 
the  upper  part  of  the  grate  and  forming  a  gas-producer  whose  action 
is  to  coke  the  fresh  fuel  and  release  its  gases,  which,  mingling  with 
heated  air,  supplied  in  small  streams  through  the  perforated  tile  above 
the  dead-plate,  are  burned  in  the  large  combustion-chamber  above  the 
bed  of  incandescent  coke  on  the  lower  part  of  the  grate. 

This  stoker  burns  all  kinds  of  coal,  from  lignite  to  anthracite,  and 
also  waste  products,  such  as  tanbark,  sawdust,  cottonseed  hulls,  and 
coke  " breeze/'  without  change  of  grate-bars. 

The  Acme  Stoker  is  shown  in  Fig.  27.  The  angle  of  the  grates 
can  be  changed  to  suit  different  coals,  and  lowering  to  a  level  with 
the  firing-doors  converts  the  stoker  into  a  hand-fired  furnace  with 
shaking-grates.  Either  bituminous  or  anthracite  coal  can  be  burned 
as  desired. 

The  stoker  consists  of  a  cast-iron  front,  the  mechanism  for  oper- 
ating the  stoker,  a  coal-hopper,  firing-doors  (to  be  used  when  the 
stoker  is  used  as  a  hand-fired  furnace),  auxiliary,  inclined,  and 
dump-grates,  stoker-frame,  brick  arch,  etc.  The  power  to  operate  is 
provided  by  an  engine  or  motor  at  the  side,  connected  direct  to  each 
stoker,  or  to  an  overhead  shaft  which  is  connected  to  each  stoker,  ar- 
ranged so  that  each  stoker  can  be  operated  separately,  or  all  together, 
as  desired.  The  coal-pusher  delivers  the  coal  from  the  hopper  to  the 
dead-plate  and  grates,  and  is  adjustable  from  nothing  to  full  capacity, 
by  turning  a  wheel  on  the  regulator. 

The  auxiliary  coking-grates,  just  in  front  of  the  dead-plate,  are 
movable  and  sectional,  and  when  put  together  form  square  boxes 
through  which  a  large*  amount  of  air  is  introduced  immediately  under 
the  fire-brick  arch,  the  reflected  heat  from  which  cokes  the  fuel  be- 
fore it  starts  down  the  inclined  grates.  The  inclined  grates  are  set  at 


FURNACES.— METHODS  OF  FIRING,  ETC. 


175 


an  angle  of  32°,  and  are  spaced  according  to  the  kind  of  fuel  to  be 
used.  Each  alternate  one  is  movable,  the  motion  being  regulated 
from  the  front.  Their  motion  is  to  rise  above  the  fixed  bars  and  then 
move  forward,  conveying  the  burning  fuel  forward,  and  then  dropping 
back  to  their  place.  By  this  means  the  coal-pusher  and  auxiliary 
grates  can  be  kept  running  and  the  inclined  grates  kept  still,  or  either 
or  both  can  be  kept  in  motion  at  the  same  time.  The  dump-grate  at 


FIG.  27.— THE  ACME  STOKER. 

the  bottom  and  end  of  the  inclined  grates  is  controlled  by  a  lever 
in  front  and  can  be  dropped  to  deposit  the  refuse  in  the  ash-pit  or  ash- 
conveyor.  « 

When  it  is  desired  to  fire  by  hand  the  inclined  grates  are  dropped 
to  a  level  with  the  firing-doors,  the  coal-hopper  lid  is  closed,  and  the 
coal  is  fed  by  hand  through  the  firing-doors  in  the  usual  way.  This 
arrangement  of  lowering  the  grates  is  convenient  in  starting  the  fires; 
a  good  fire  can  be  started  in  the  ordinary  way  with  the  grates  lowered, 
and  when  the  bed  of  coal  is  fully  ignited,  the  grates  can  be  raised  and 
;the  stoker  put  in  operation. 


176 


STEAM-BOILER  ECONOMY. 


The  "Wilkinson  Stoker  is  shown  in  Fig,  28.  Its  peculiar  feature 
is  the  use  of  hollow  grate-bars  through  which  air  is  forced  by  means 
of  small  steam-jets.  The  bars  are  inclined  at  an  angle  of  25°  to  the 


LONG  HYDRO-CARBONACEOUS 
WATER  GAS   FLAME 


FIG.  28.— THE  WILKINSON  STOKER. 

horizontal.  Adjacent  bars  are  moved  in  opposite  directions  by  a  sys- 
tem of  toggles  controlled  by  gearing  driven  by  the  stoker-engine.  An 
account  of  some  tests  of  this  stoker,  with  rice  coal,  made  by  J.  M. 
Whitham,  will  be  found  in  Trans.  Am.  Soc.  M.  E.,  vol.  xvii.  p.  561. 
The  Murphy  Automatic  Furnace  is  shown  in  cross-section  as  ap- 
plied to  a  horizontal  tubular  boiler  in  Fig.  29.  The  furnace  is  also 
applicable  to  all  forms  both  of  fire-tube  and  water-tube  boilers.  The 
grates  are  of  a  "V  "  form  and  in  pairs,  the  upper  ends  resting  on  the 
magazine  bed-plate,  which  is  also  the  feed-  or  coking-plate,  while  the 
lower  ends  rest  in  niches  on  the  grate-bearer,  which  also  contains 
the  clinker-bar  or  clinker-breaker.  A  fire-bri^k  arch  is  sprung  across 
the  furnace,  covering  the  grate-surface,  and  on  top  of  each  side  of  the 
arch  there  is  an  air-flue  from  which  hot  air  is  supplied  through  the 
series  of  small  openings  at  the  bases  of  the  arch  where  the  brick  rests 
on  the  ribbed  surface  of  the  arch-plates  on  either  side  of  the  furnace. 
This  gives  a  double  side  feed-  and  coking-plate.  The  coal  magazines 
are  provided  with  stoker-boxes,  which  are  connected  by  means  of  pin- 
ion-gears to  the  stoker-shaft,  which  ^s  automatically  moved  back  and 


FURNACES.— METHODS  OF  FIRING,  ETC. 


177 


forth,  stoking  the  coal  into  the  furnace.  One  grate  of  each  pair  of 
grates  is  fixed,  while  the  other  is  movable  up  and  down  by  a  rocker 
motion  at  the  lower  or  centre  end,  thus  keeping  the  fire  free  from 
ashes  while  the  coarse  refuse  and  clinker  is  worked  down  to  the  centre, 
where  a  rotating  clinker-bar  grinds  it  into  the  ash-pit.  The  entire 
operating  mechanism  is  attached  to  a  flat  iron  bar  running  across  the 


FIG.  29. — THE  MURPHY  AUTOMATIC  FURNACE. 

outside  of  the  front,  and  operated  by  a  little  automatic  upright  engine 
set  at  the  corner  of  the  setting,  which  uses  about  one  horse-power  per 
furnace  operated.  Each  revolution  of  the  driving- gear  stokes  a  given 
but  variable  quantity  of  coal  into  the  furnace  on  each  side,  moves  half 
of  the  grate-bars  on  each  side  up  and  down,  and  turns  the  clinker-bar 
partly  around.  Thus  the  coal  is  fed  and  the  fires  cleaned  constantly. 
The  teeth  on  the  clinker-bar  are  prevented  from  becoming  hot  and 
worn  off  by  means  of  a  current  of  air  passing  through  the  open  centre 
of  the  bar  and  piped  to  the  flue  or  stack  beyond  the  damper. 

The  clinker  is  kept  brittle  and  prevented  from  sticking  by  a  spray 
of  exhaust  steam  distributed  through  a  pipe  cast  into  either  side  of 
the  grate-bearer. 

The  American  Stoker  is  shown  in  longitudinal  section  in  Fig.  30 
and  in  cross-section  in  Fig.  31.  By  this  stoker  the  fresh  coal  is  fed 
underneath  the  bed  of  burning  coal,  being  pushed  upward  from  a  deep 
trough  with  rounded  bottom  by  means  of  a  tapering  screw,  which  is 


178 


STEAM-BOILER  ECONOMY. 


driven  by  an  independent  steam-motor.  The  motor  is  the  steam  end 
of  a  small  direct-acting  steam-pump.  Below  the  coal- trough  there  is 
an  air-box,  from  which  air  is  delivered  under  pressure  through  a  series 


FIG.  30. — THE  AMERICAN  STOKER. 

of  heavy  cast-iron  tuyeres  at  the  level  of  the  top  of  the  trough.  The 
jets  of  air  are  delivered  horizontally,  crossing  each  other,  and  cutting 
through  the  rounded  bed  of  hot  coal  lying  above.  The  volatile  matter 
is  distilled  from  the  coal  in  the  upper  part  of  the  trough  and  passes 


FIG.  31. — THE  AMERICAN  STOKER. 

with  the  air  through  the  bed  of  hot  coke  above,  burning  without 
smoke  if  the  air-supply  is  properly  adjusted  to  the  rate  of  feed  of  the 
coal.  The  space  on  each  side  of  the  stoker,  between  the  tuyere-blocks 
and  the  side  walls  of  the  furnace,  is  occupied  by  dead-plates  or  grates. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


179 


The  ash  fuses  into  a  clinker  and  accumulates  on  the  dead-plates  in 
large  lumps,  which  are  easily  removed.  This  stoker  has  had  a  very 
successful  career  with  highly  volatile  coals  of  the  West,  and  also  .in  the 
East  with  semi-bituminous  coals.  Furnaces  over  6  feet  in  width  are 
equipped  with  a  double  stoker.  This  is  a  combination  of  two  single 
stokers  feeding  from  a  common  hopper  and  operated  by  a  single 
motor. 

The   Jones  Under-feed  Stoker  (Figs.  32  and  33)  was  patented  m 


FIG.  32. — THE  JONES  UNDER-FEED  STOKER. 

1896  by  E.  W.  Jones  of  Portland,  Oregon.  The  fresh  coal  is  pushed 
up  through  the  bed  of  burning  fuel  by  means  of  a  steam-ram,  oper- 
ated by  a  hand-lever  connected 
to  a  valve,  by  means  of  which  the 
charges  of  fuel  can  be  delivered  as 
required.  Air  at  about  four  ounces 
pressure  is  forced  through  the 
tuyere-blocks,  and  up  through  the 
heap  of  burning  fuel,  and,  ming- 
ling with  the  gases  from  the  cok- 
ing coal,  produces  an  intense  and 

rapid  combustion.     Owing  to  the 

i  -    .    ,  ,.         j     .  i  •  i         FlG-  33.— CYLINDER  OF  THE  JONES 

large  excess  of  air  delivered  at  high  STOKER. 

pressure,  and  its  thorough  mingling  with  the  gases,  a  practically  smoke- 
less combustion  is  obtained.  This  stoker  has  been  principally  used  with 
low-grade  Western  American  bituminous  slack  coal. 

Forced  Draft.— The  use  of  forced  draft,  as  a  substitute  for,  or  as  an 
aid  to,  natural  chimney  draft,  is  becoming  quite  common  in  large 
boiler-plants.  Its  advantages  are  that  it  enables  a  boiler  to  be  driven 


180  STEAM-BOILER  ECONOMY. 

to  its  maximum  capacity  to  meet  emergencies  without  reference  to  the 
state  of  the  weather  or  to  the  character  of  the  coal;  that  the  draft 
is  independent  of  the  temperature  of  the  chimney  gases,  and  that 
therefore  lower  flue  temperatures  may  be  used  than  with  natural  draft; 
and  in  many  cases  that  it  enables  a  poorer  quality  of  coal  to  be  used 
than  is  required  with  natural  draft. 

Forced  draft  may  be  obtained :  First,  by  a  steam- jet  in  the  chimney, 
as  in  locomotives  and  steam  fire-engines;  second,  by  a  steam-jet  blower 
under  the  grate-bars;  third,  by  a  fan-blower  delivering  air  under  the 
grate-bars,  the  ash-pit  doors  being  closed ;  fourth,  by  a  fan-blower  de- 
livering air  into  a  closed  fireroom,  as  in  the  "  closed  stokehold"  sys- 
tem used  in  some  ocean-going  vessels;  and  fifth,  by  a  fan  placed  in  the 
flue  or  chimney  drawing  the  gases  of  combustion  from  the  boilers, 
commonly  called  the  induced  draft  s}7stem.  Which  one  of  these  several 
systems  should  be  adopted  in  any  special  case  will  usually  depend  on 
local  conditions.  The  steam- jet  has  the  advantage  of  lightness  and 
compactness  of  apparatus,  and  is  therefore  most  suitable  for  locomo- 
tives and  steam  fire-engines,  but  it  also  is  the  most  wasteful  of  steam, 
and  therefore  should  not  be  used  when  a  fan-blower  system  is  available,, 
except  for  occasional  or  temporary  use,  or  when  very  cheap  fuel,  such 
as  anthracite  culm  at  the  coal-mines,  is  used. 

The  closed  stokehold  system  has  as  yet  been  used  only  in  marine 
practice,  where  it  has  some  advantage,  such  as  ventilation  of  the  fire- 
room,  over  the  closed  ash-pit  system.  Induced  draft  has  been  used  to 
some  extent  on  land,  with  good  results,  but  it  does  not  appear  to  have 
any  especial  advantage  over  the  closed  ash-pit  system,  except  conven- 
ience of  application  in  some  situations,  as  where  an  exhaust-fan  can  be 
placed  in  the  chimney  more  easily  than  a  fan-blower  of  sufficient  size 
can  be  accommodated  in  the  boiler-  or  engine-room.  In  a  crowded  and 
poorly  ventilated  fireroom  a  fan-blower  delivering  air  under  the  grates 
and  maintaining  a  pressure  of  gas  in  the  furnace  may  sometimes  cause 
objectionable  gases  and  dust  to  issue  into  the  fireroom,  and  in  such  a 
case  induced  draft  may  be  preferable. 

When  an  economizer  is  used  to  absorb  some  of  the  heat  escaping 
from  the  boilers,  it  is  generally  advisable  to  use  forced  draft,  since  the 
lower  temperature  of  the  gases  discharged  from  the  economizer  reduces 
the  force  of  draft  in  the  chimney  and  the  friction  of  the  gas  passages 
through  the  economizer  itself  reduces  the  force  of  draft  at  the  boiler. 

Forced  draft  is  especially  valuable  in  large  boiler-plants,  such  as 
those  of  electric  light  and  power  stations,  where  the  demand  for  steam 


FURNACES.— METHODS   OF  FIRING,  ETC.  181 

is  much  greater  during  a  few  hours  in  the  day  than  during  the  rest 
of  the  time.  A  boiler-plant  which  would  be  insufficient  with  natural 
draft  to  supply  the  steam  required  during  the  hours  of  heaviest  load, 
may  be  able  to  supply  it  with  ease  by  the  aid  of  forced  draft. 

When  forced  draft  is  used,  it  is  advisable  to  provide  it  with  auto- 
matic regulation,  the  delivery  of  steam  to  the  engine  driving  the  fan 
being  regulated  by  a  reducing- valve,  or  a  cut-oif  valve,  controlled  by 
the  pressure  in  the  boiler,  as  in  the  Beckman  system.  This  system 
consists  of  a  fan-blower,  driven  by  a  small  engine,  delivering  air  into  a 
conduit  built  under  the  bridge  wall,  which  conduit  may  be  common  to 
a  battery  of  boilers,  and  thence  through  openings  into  the  ash-pit 
under  the  grate  of  each  boiler.  In  the  steam-pipe  leading  to  the  en- 
gine there  are  three  valves.  The  first  automatically  opens  or  closes  as 
the  steam-pressure  falls  or  rises.  The  second  is  a  reducing- valve  which 
delivers  to  the  engine  steam  of  the  pressure  required  to  drive  the  en- 
gine at  the  right  speed  for  furnishing  the  air  to  burn  the  particular 
kind  of  fuel  used.  The  third  is  a  by-pass  valve  which  lets  enough 
steam  into  the  engine  while  the  first  valve  is  closed  to  keep  the  engine 
just  moving  and  furnishing  enough  air  to  keep  the  grates  cool.  The 
damper  leading  from  the  air-conduit  into  the  ash-pit  is  closed  when 
the  boiler  is  out  of  use  or  during  cleaning. 

The  Howden  Hot-air  System. — In  1884  Mr.  J.  Howden  applied  to 
the  boilers  of  the  City  of  New  York  a  forced  draft  apparatus  in 
which  the  air-supply  was  heated  by  being  circulated  around  a  series 
of  tubes,  through  which  the  hot  flue-gases  passed  on  their  way  to 
the  stack.  In  this  system  part  of  the  hot  air  is  delivered  into  the  ash- 
pit, and  part  above  the  bed  of  coal  in  the  furnace.  The  system  has 
been  extensively  adopted  in  marine  practice.  Among  the  advantages 
claimed  for  it  are:  1.  Part  of  the  heat  which  would  otherwise  escape  in 
the  flue-gases  is  returned  to  the  boiler.  2.  By  whatever  amount  the  air 
for  combustion  is  increased  in  temperature  by  the  waste  gases,  the 
average  temperature  of  the  furnaces  is  practically  raised  to  the  same 
extent.  If,  say,  200°  is  added  to  the  air  of  combustion  by  the  air-heat- 
ers, the  average  temperature  of  the  furnaces  is  raised  200°,  and  the 
evaporative  power  of  the  heating  surface  is  thereby  increased.  3.  The 
gases  from  the  burning  fuel  combine  more  readily  with  the  oxygen  of 
the  air  of  combustion  as  the  temperature  of  the  fire  increases. 

Retarders. — In  connection  with  the  Howden  system,  spiral  strips 
of  metal,  shown  in  Fig.  34,  are  placed  in  the  tubes  of  the  boiler. 
These  compel  the  gases  to  take  a  spiral  motion  in  passing  through  the 


182 


STEAM-BOILER  ECONOMY. 


tubes,  causing  them  to  come  more  directly  in  contact  with  the  sur- 
face of  the  tubes,  and 

through  the  metal  of 

the  retarder  into  the  FIG.  34.— A  RETAHDEK. 

metal  of  the  tubes  increasing  their  efficiency. 

Results  of  tests  of  a  horizontal  fire-tube  boiler  with  and  without 
retarders  are  given  in  a  paper  by  J.  M.  Whitham  in  Trans.  A.  S.  M.  E., 
vol.  xvii.  p.  450.  Among  his  conclusions  are  the  following: 

1.  Retarders  show  an  economic  advantage  when  the  boiler  is  pushed, 
varing  in  the  tests  from  3  to  18  per  cent. 

2.  Retarders  should  not  be  used  when  boilers  are  run  very  gently 
and  when  the  stack-draft  is  small. 

The  Ellis  &  Eaves  Hot-air  System  is  similar  to  Howden's,  but  the 
draft  is  produced  by  a  fan  placed  at  the  base  of  the  funnel.  The  air 
is  heated  by  being  passed  through  the  tubes  in  the  heater,  while  the 
hot  gas  circulates  around  them.  Both  the  Howden  and  the  Ellis  & 
Eaves  systems  are  illustrated  and  discussed  at  length  in  Bertin  & 
Robertson  on  "  Marine  Boilers." 

An  extensive  series  of  experiments  on  the  use  of  warm  blast  was 
made  by  J.  C.  Hoadley  in  1881,  and  described  at  great  length  in 
Trans.  Am.  Soc.  M.  E.,  vol.  vi.  p.  676.  The  results,  according  to  Mr. 
Hoadley,  showed  a  possible  net  saving  of  from  10  to  18  per  cent  over 
the  best  attainable  practice  with  natural  chimney  draft  and  air  at 
ordinary  atmospheric  temperatures.  Notwithstanding  these  results,  the 
warm-blast  system  has  not  as  yet  made  any  headway  in  land  practice. 


FIG.  35.— METHOD  OF  BUENTNG  COAL-DUST. 

Furnaces    for    Burning   Coal-dust. — Fig.    35   shows    a    coal-dust 
stoker  patented  in  1895  by  F.  De  Camp  of  Berlin,  Germany.      The 


FURNACES.— METHODS  OF  FIRING,  ETC. 


183 


coal  is  ground  in  a  mill  and  carried  to  the  hopper  of  the  stoker  by  a 
travelling  conveyor,  from  which  it  is  delivered  into  the  furnace  by  a 
fan-blast.  The  quantity  of  coal-dust  as  well  as  the  quantity  of  air 
blown  into  the  furnace  is  regulated  by  slides.  The  advantages  claimed 
for  the  apparatus  are  that  it  is  an  automatic  stoker  and  forced-draft 
system  combined,  and  that  the  combustion  is  complete  and  smokeless. 

The  objections  are,  the  cost  of  power  for  grinding  the  coal  into  a 
fine  powder  and  for  driving  the  fan,  together  with  the  extra  labor  re- 
quired to  keep  the  flues  clean,  on  account  of  the  large  accumulation  of 
ash  and  partially  burned  coal-dust  which  is  carried  over  by  the  blast. 

The  Wegener  Apparatus  for  Burning  Powdered  Coal. — Fig.  36 
shows  an  apparatus  for  burning  powdered  coal,  invented  by  Carl 
Wegener,  and  first  used  in  Ger- 
many in  1892.  It  is  described  as 
follows: 

Coal  ground  so  that  it  will  pass 
through  a  sieve  of  125  meshes  per 
linear  inch  is  fed  into  the  hopper, 
whence  it  falls  on  to  a  fine  sieve 
about  5|  in.  diameter.  The  sieve 
is  tapped  from  150  to  250  times  a 
minute,  in  order  to  cause  the  coal 
to  fall  through  it  regularly,  by 
means  of  a  knocker  on  a  vertical 
shaft  driven  by  awheel  placed  in 
the  path  of  the  entering  air-sup- 
ply. The  air  ascending  in  the 
inlet-pipe,  as  shown  in  the  cut, 
meets  the  descending  shower  of 
powdered  coal,  mixes  with  it,  and 
carries  it  into  the  furnace.  If 
the  air-supply  is  sufficient,  smoke- 
less combustion  will  result. 

Records  of  tests  of  the  Wege- 
ner apparatus*  indicate  that  it 
does  not  give  any  higher  economy 
than  can  be  obtained  by  mechani-    FlQ  36  _WEOENER,S  PowDERED  CoAL 
cal    stokers,  or   other   means   of  APPARATUS, 

burning  soft  coal,  which  do  not  require  the  coal  to  be  powdered. 


'Revolving  Air  Wheel 
or  Turbine 


Engineering  News.  Sept.  16,  1897. 


184  STEAM-BOILER  ECONOMY. 

Methods  of  Burning  Petroleum.*  —  The  simplest  and  best  way  of 
burning  liquid  fuel  is  by  injecting  it  in  the  form  of  spray  by  means  of 
a  jet  of  steam  into  the  furnace  and  allowing  the  right  amount  of  air 
to  mix  with  it.  The  number  of  different  injectors  or  burners  that 
have  been  devised  for  this  purpose  is  legion. 

The  simplest  device  would  consist  of  two  tubes  fastened  together, 
as  shown  in  the  annexed  sketch,  Fig.  37.  In  this,  1  is  the  oil  feed- 
pipe; 2,  a  cock  for  regulating  supply  of  oil;  3,  the  steam  -pipe  ;  4,  the 

valve  for  regulating  supply 
of  steam  ;  5,  a  guard  around 
pipe  preventing  overflow. 
The  lower  tube  is  flattened 
out  to  a  thin,  broad  open- 
ing, from  which  the  stream 


allows  a  stream  of  oil  to  flow  from  the  supply-tank,  this  flow  being 
regulated  by  the  supply-cock.  The  oil  is  conducted  by  the  guard,  5, 
which  prevents  it  flowing  over  the  sides  of  the  lower  steam-pipe,  and 
distributes  it  in  a  thin  sheet  over  the  rapidly  issuing  steam,  with  the 
result  that  the  oil  is  rapidly  carried  forward  in  the  form  of  a  finely 
divided  spray,  which  is  the  next  thing  to  gas,  and  ignites  almost  as 
easily.  By  changing  the  shape  of  the  issuing  jet  of  steam,  different 
shapes  may  be  given  to  the  flame.  If  we  give  the  steam-jet  a  fan- 
shaped  opening,  the  greater  part  of  the  oil  will  be  delivered  at  the 
sides  and  we  will  have  a  wide  and  short  flame.  If,  on  the  contrary, 
we  desire  a  long,  narrow  flame,  we  give  the  steam-jet  a  concave 
opening,  then  most  of  the  oil  is  delivered  on  the  centre  of  the  steam- 
jet  and  is  propelled  forward  to  a  considerable  distance. 

Those  who  try  to  improve  the  efficiency  of  a  fuel  by  altering  the 
burner  resemble  a  man  who  seeks  to  improve  the  steaming  of  his  boiler 
by  changing  the  injector.  The  place  to  work  at  and  improve  is  inside 
the  fire-box  or  combustion-chamber.  The  oil  fuel  must  be  so  broken 
up  or  pulverized  as  to  allow  of  its  mixing  with  the  air  and  being  in- 
stantly consumed.  If  it  is  not  consumed  in  the  fire-box,  it  issues 
either  in  the  form  of  smoke  or  of  foul-smelling,  unburned  gases,  and 
fuel  is  wasted. 

If  we  take  a  vessel  filled  with  benzine  and  set  fire  to  it,  it  burns 
with  a  heavy  flame,  and  large  quantities  of  black  smoke  are  given  off. 
As  no  air  can  get  to  the  interior  portion,  combustion  takes  place  on 
the  outside,  and  as  the  contained  hydrogen  has  a  greater  affinity  for 
oxygen  than  carbon,  it  combines  with  most  of  the  oxygen  furnished 
by  the  air,  the  carbon  is  set  free  and  is  visible  in  the  form  of  a  heavy, 
black  smoke. 

If  we  admit  air  to  the  interior  of  the  volatile  gases  which  are  be- 
ing given  off,  more  oxygen  is  supplied  and  part  of  the  carbon  burns 
and  the  smoke  diminishes,  and  if  arrangements  are  made  so  as  to  ad- 

*  Extracts  from  a  paper  by  H.  Tweddle,  in  The  Engineering  and  Mining  Jour- 
nal, Oct.  21,  1899. 


FURNACES—METHODS  OF  FIRING,  ETC. 


185 


mit  sufficient  air  to  all  parts  of  the  benzine  and  its  vapor,  then  we  will 
have  complete  combustion  and  no  smoke  will  be  given  off. 

In  order  to  obtain  the  greatest  efficiency  from  fuel  oil,  it  should 
be  burned  in  a  fire-brick  combustion-chamber,  so  as  to  obtain  the  very 
highest  possible  temperature.  Notwithstanding  the  fact  that  a  cer- 
tain amount  of  heating  surface  is  covered  by  the  brickwork,  experi- 
ments have  shown  that  there  is  both  an  increase  in  evaporation  and  a 
saving  in  fuel  with  the  lined  fire-box. 

Use  of  Petroleum  in  Locomotives. — Mr.  Tweddle  describes  the  use  of 
petroleum  as  fuel  for  locomotives  on  the  Oroya  Railroad,  in  Peru, 
where  he  introduced  it  in  1890.  Two  locomotives,  exactly  alike  in  all 
other  respects,  were  tested,  one  with  coal  and  the  other  with  oil. 
They  were  American  Rogers  engines,  Mogul  type,  with  47  in.  drivers; 
cylinders  18x24  in.;  weight  of  engine  38  tons,  tender  28  tons;  five 
cars  averaging  18  tons  each.  The  grades  were  as  high  as  4.2  per  cent, 
or  1  in  27,  with  some  sharp  curves.  The  average  consumption  of  coal 
for  a  month  was  79.30  Ibs.  per  train  mile,  and  that  of  oil  38.55  Ibs.,  or 
less  than  half. 

The  arrangement  for  the  interior  of  the  fire-box  is  shown  in  Fig. 
38.  No  alterations  were  made  in  the  fire-box,  while  but  few  additions 


FTG.  38. — PETROLEUM  FURNACE. 


FIG.  39. — OIL-BURNER. 


were  made  to  the  regular  ash-pan.  The  back  damper  was  completely 
closed,  a  large  front  damper  with  about  2  sq.  ft.  superficial  opening 
being  arranged  in  front.  A  plate  with  an  air-opening  20  X  14  in.  sup- 
ported the  fire-brick  at  the  back  of  the  fire-box,  which  receives  the 
vaporized  oil. 

In  Fig.  39,  the  burner  is  represented.  A  is  a  general  side  view  of 
burner;  at  g  it  is  tapped  for  a  l-|-in.  oil-pipe,  and  at  h  for  a  J-in. 
steam-pipe.  In  the  sectional  view,  e  e  is  the  oil-passage,  d  d  is  the 
steam-passage;  both  these  passages  being  3  by  f  in.  D  represents  the 
front  end  of  the  burner,  and  E  represents  the  back  end  of  the  burner. 

The  oil  coining  through  the  passage,  e  e,  falls  directly  on  the  steam 


186  STEAM-BOILER  ECONOMY. 

shooting  through  the  narrow  slit  at  the  end  of  the  passage,  d  d,  and  is 
completely  atomized. 

With  this  burner  the  bricks  do  not  serve  in  any  way  for  breaking 
up  the  oil,  but  merely  as  a  white-hot  retort  in  which  air  and  vaporized 
oil  are  mixed  in  the  proper  proportions.. 

The  supply  of  air  is  regulated  by  the  front  damper,  the  supply  of 
oil  by  a  wheel-valve  worked  by  the  fireman's  hand  in  the  cab.  The 
steam  is  seldom  touched  except  when  an  engine  is  lying  up  for  any 
length  of  time  at  a  station.  With  the  oil  and  air  under  such  easy 
control  there  is  no  difficulty  in  obtaining  perfect  combustion  without 
smoke. 

The  holes  at  the  back  of  the  burner  are  closed  with  plugs.  By 
unscrewing  these  the  burner  can  be  quickly  cleaned  without  remov- 
ing; this,  however,  is  rarely  necessary,  the  burner,  as  a  rule,  keeping 
perfectly  clean  for  an  indefinite  period. 

The  burner  is  cast  in  one  piece  and  finished  by  hand.  The  length 
of  the  burner  is  entirely  arbitrary.  The  width  is  made  to  suit  the 
quantity  of  fuel  to  be  introduced. 

On  the  heavy  grades  of  the  Oroya  line,  as  much  as  220  Ibs.  of  coal 
are  burned  per  mile,  or  110  Ibs.  of  oil.  To  perfectly  spray  such  a 
large  flow  of  oil,  a  certain  width  of  passage  is  necessary.  The  burner 
best  adapted  to  such  heavy  work  had  an  oil-passage  3  in.  wide  and  a 
steam-outlet  of  3£  in.  The  oil-aperture  was  3  by  f  in.,  the  steam- 
aperture  3J  by  TV  in. 

Around  the  oil-opening  runs  a  sort  of  projecting  hood  which  pre- 
vents any  oil  from  leaking  when  rounding  sharp  curves.  Steam  from 
another  locomotive  is  used  in  getting  up  steam;  100  Ibs.  pressure 
from  cold  water  has  been  shown  on  the  steam-gauge  in  25  minutes, 
but  an  hour  is  generally  taken,  so  as  not  to  strain  the  boiler.  If  neces- 
sary wood  can  be  used  to  raise  steam. 

The  oil-fired  engine,  after  running  six  months,  showed  no  signs  of 
leaking  or  straining.  About  150  fire-brick  were  used  for  the  whole 
brickwork,  including  the  arch.  This  brickwork  lasts  from  six  to 
eight  months. 

The  Urquhart  Oil-burner,  used  in  locomotives  in  Eussia,  is  shown 
in  Fig.  40.  The  oil  runs  down  a  pipe,  which  ends  in  the  external 
nozzle  of  the  injector,  while  the  steam  passes  through  the  inner  nozzle, 
which  it  enters  through  a  ring  of  holes,  the  steam-  and  oil-cavities 
being  separated  by  a  stuffing-box  packed  with  asbestos.  This  pack- 
ing is  renewed  once  a  month.  The  steam-supply  is  regulated  by  a 
valve,  and  the  oil-supply  by  screwing  the  steam-nozzle  backward  and 
forward  in  the  external  nozzle,  thus  varying  the  section  of  the  annular 
passage.  This  is  effected  by  a  worm  and  worm-wheel,  the  latter  of 
which  is  connected  to  the  steam-nozzle  by  a  feather-key,  while  the 
former  is  on  a  shaft  which  terminates  in  a  position  conveniently  acces- 
sible to  the  fireman.  The  injector  is  entirely  outside  of  the  fire-box, 


FURNACES.— METHODS  OF  FIRING,   ETC. 


187 


so  that  the  carbonizing  of  the  oil  at  the  nozzle  is  reduced  to  a  mini- 
mum. The  blast  of  oil  and 
steam  is  delivered  into  the 
furnace  through  a  tube  into 
which  the  nose  of  the  injector 
projects,  and  through  which 
a  supply  of  air  is  also  drawn 
by  the  action  of  the  jet. 

The  amount  of  steam  re- 
quired to  operate  the  injector 


FIG.  40. — THE  URQUHART  OIL-BURNER. 


on   the   Russian    railway,   ac- 
cording to  Mr.   Urquhart,  is 
from  8  to  13  per  cent  of  the  steam  made  by  the  boiler,  the  highest 
percentage  being  required  in  winter. 

Furnaces  for  Burning  Green  Bagasse  and  other  substances  con- 
taining a  great  deal  of  water,  such  as  wet  tan-bark,*  require  very  large 

fire-brick  combustion-chambers^ 
in  order  to  give  plenty  of  room 
and  time  for  the  combustion  of 
the  distilled  gases  before  they  are 
allowed  to  reach  the  heating  sur- 
faces of  the  boiler.  The  fuel 
should  be  fed  either  in  small 
quantities  at  a  time  or  else  in  a 
steady  stream,  so  that  the  evap- 
oration of  its  moisture  may  pro- 
ceed at  a  uniform  rate  and  chill 
the  furnace  as  little  as  possible. 
Fig.  40$  shows  an  end  view  of 
Cook's  bagasse  burner,  placed 
FIG. 40a.—  BAGASSE  FURNACE,  END  VIEW,  between  two  water-tube  boilers. 
It  will  be  observed  that  the  structure  is  larger  than  the  boiler-setting 
in  end  view,  and  its  length  is  also  much  greater  than  that  of  the 
boiler-setting.  It  consists  of  a  large  fire-brick  oven  with  a  smaller 
chamber  beneath.  In  the  rear  of  the  oven,  between  it  and  the 
chimney,  a  tubular  heater  is  placed,  in  which  the  air-supply  is  heated 
by  the  gases  on  the  way  from  the  boiler  to  the  chimney.  The  fuel  is 
delivered  to  the  furnace  automatically,  by  means  of  a  conveyor. 


*  For  experiments  on  tan-bark  furnaces  see  page  136. 


CHAPTER  VIII. 

SOME    ELEMENTARY    PRINCIPLES    OF    STEAM-BOILER    ECONOMY 
AND    CAPACITY— THE   PLAIN   CYLINDER   BOILER. 

IK  this  chapter  we  will  discuss  by  a  somewhat  elementary  method, 
without  the  use  of  any  algebraic  formula,  the  principles  upon  which 
depend  the  economy  and  the  capacity  of  the  heating  surface  of  a  steam- 
boiler,  using  for  illustration  the  plain  cylinder  boiler.  In  the  suc- 
ceeding chapter  the  same  subject  will  be  treated  in  another  manner, 
with  the  use  of  some  mathematics.  The  conditions  which  determine 
to  a  great  extent  how  large  a  boiler,  or  battery  of  boilers,  should  be 
used  for  a  given  purpose  are:  The  quantity  of  steam  required;  the 
quality  and  the  cost  of  fuel;  the  degree  of  fuel  economy  desired;  the 
quality  of  the  water  supplied ;  the  regularity  of  the  demand  for  steam ; 
the  size  and  shape  of  the  space  available,  etc. 

Let  us  consider  how  the  size  and  form  of  a  boiler  are  governed  by 
the  conditions  of  quantity  of  steam  required  and  by  the  degree  of  fuel 
economy  desired. 

Instead  of  taking  the  problem  that  is  usually  presented,  viz. :  "  A 
certain  quantity  of  steam  is  required,  what  shall  be  the  form  and  size 
of  the  boiler  to  furnish  it?"  it  will  better  serve  the  purpose  of  ele- 
mentary instruction  to  state  the  problem  in  the  reverse  manner,  viz. : 
"  Given  the  form  and  size  of  a  certain  boiler,  how  much  steam  will  it 
furnish?" 

Capacity  of  a  Plain  Cylinder  Boiler.— We  will  begin  the  study  of 
this  problem  by  taking  an  example  of  the  simplest  form  of  boiler,  a 
plain  cylinder  of  a  size  that  is  still  commonly  used  at  anthracite  coal- 
mines, viz:  30  in.  diameter  and  30  ft.  long.  It  is  provided  with  a 
setting  of  brick-work,  the  side  walls  being  3  feet  apart,  and  with  an 
ordinary  grate,  3  ft.  wide  and  4  ft.  long,  or  12  sq.  ft.  of  grate-surface. 
At  the  rear  end  there  is  a  flue  leading  to  a  tall  chimney.  The  side 
walls  of  the  setting  are  built  in  at  the  top  so  as  to  touch  the  boiler  at 

the  middle  of  its  height,  so  that  only  one-half  of  the  boiler  is  exposed 

188 


ELEMENTARY  PRINCIPLES—  THE  PLAIN  CYLINDER  BOILER. 


to  radiation  from  the  fire  and  to  contact  with  the  heated  gases.     The 
water-level  is  carried  a  few  inches  above  the  middle  of  the  boiler,  so 


FIG.  41. — PLAIN  CYLINDER  BOILEB. 

that  at  'no  time  is  any  part  of  the  external  surface  of  the  boiler  ex- 
posed to  the  flame  or  heated  gases  without  having  water  on  the  oppo- 
site inner  surface.  The  boiler  is  made  of  steel,  ^  inch  thick,  which  is 
ample  for  strength,  and  is  supposed  to  be  kept  free  from  scale  on  the 
inside  and  from  deposits  of  soot  and  ashes  on  the  outside.  The  up- 
per half  of  the  boiler,  above  the  brick  walls,  is  covered  with  a  non- 
conducting covering,  to  prevent  excessive  loss  of  heat  by  radiation. 
Such  a  boiler  is  shown  in  Fig.  41. 

The  boiler  being  30  ft.'  long  and  2|-  ft.  external  diameter,  and  the 
lower  half  of  its  surface  being  heating  surface,  the  area  of  the  heating 
surface  is  \  of  30  X  2|  X  3.1416  =  117.81  sq.  ft.  We  can  make  this 
120  ft.  by  letting  the  side  walls  touch  the  heating  surface  |  in.  above 
the  middle  of  the  boiler;  or,  if  we  let  them  extend  7-J  in.  above  the 
middle,  raising  the  water-level  to  correspond,  until  it  is  within  5  or  6 
in.  of  the  top  of  the  boiler,  we  can  make  the  heating  surface  equal  to 
two-thirds  of  the  whole  external  cylindrical  surface  of  the  boiler,  or 
157  sq.  ft.  This  will,  however,  not  be  generally  advisable,  since  by 
bringing  the  water-level  so  close  to  the  top  of  the  boiler  there  would 
be  danger  of  carrying  water  into  the  steam-pipe,  making  what  is 
known  as  "wet  steam."  For  the  purpose  of  this  calculation,  there- 
fore, we  will  consider  the  heating  surface  as  120  sq.  ft.  The  grate- 
surface  being,  as  already  stated,  12  sq.  ft.,  the  ratio  of  heating  to 
grate -surf  ace,  which  ratio  is  a  term  commonly  used  in  describing 
steam-boiler  proportions,  is  10  to  1. 

This  simple  form  of  boiler,  when  properly  built  and  erected,  sup- 
plied with  good  water,  and  well  taken  care  of,  has  many  excellent  quali- 
ties, which  have  caused  it  to  remain  a  favorite  form  of  boiler  in  some 
parts  of  the  world,  and  especially  in  the  anthracite  coal  regions  of  Penn- 
sylvania, ever  since  high-pressure  steam  began  to  be  used  in  steam- 
engines,  a  century  ago.  Its  disadvantages,  which  have  caused  it  to  be 


190  STEAM-BOILER  ECONOMY. 

generally  displaced  by  other  forms,  will  be  treated  of  later.  The 
study  of  the  chief  conditions  which  govern  boiler-capacity  and  boiler- 
economy  can  be  more  easily  begun  by  reference  to  this  form  of  boiler 
than  to  any  other,  and  it  is  for  this  reason  that  it  has  been  selected  for 
discussion  in  this  place,  The  theoretical  principles  which  may  be 
developed  in  treating  of  this  boiler  will  apply  in  great  measure  to  all 
other  forms  of  boilers. 

Having  thus  described  the  boiler,  we  are  now  ready  to  take  up  the 
question,  "How  much  steam  will  it  furnish?"  A  direct  answer  to 
the  question  is:  "  That  depends  on  circumstances,  and  especially  upon 
the  amount  and  upon  the  quality  of  coal  that  is  burned  under  it. 
One  boiler  of  the  form  and  dimensions  here  given  may  furnish  three 
or  four  times  as  much  steam  as  another  boiler  exactly  like  it."  This 
answer  is  correct,  but  it  is  not  sufficiently  definite  for  our  purpose. 
If  the  capacity  of  the  boiler  depends  upon  circumstances,  we  wish  to 
know,  with  some  approach  to  accuracy,  what  the  boiler  will  do  under 
different  sets  of  stated  conditions,  and  how  the  conditions  affect  the 
capacity  of  the  boiler  and  at  the  same  time  the  economy  of  fuel. 

We  will  begin  this  study  by  assuming  that  under  all  the  different 
conditions  now  to  be  considered  the  steam-pressure  is  maintained  at 
100  Ibs.,  not  by  means  of  a  damper  regulator,  which  is  occasionally 
used,  but  by  the  discharge  of  the  steam  into  a  steam-main  fed  also  by 
other  boilers  in  which  main  the  steam-pressure  is  maintained  constant 
under  a  possible  varying  demand  by  means  of  varying  the  rate  of 
driving  of  the  other  boilers  than  the  one  being  considered.  The  uni- 
formity of  pressure  might  also  be  obtained  by  having  the  steam  escape 
through  a  loaded  valve,  similar  to  a  safety-valve,  which  is  set  so  as  to 
open  whenever  the  pressure  is  100  Ibs.,  and  to  shut  below  that  pressure. 
We  will  also  assume  that  the  feed-water  is  supplied  at  a  tempera- 
ture of  155°  Fahrenheit.  These  two  assumptions  are  made  merely 
for  the  purpose  of  simplifying  the  problem,  and  thereby  shortening  to 
some  extent  the  arithmetical  computations  involved.  To  evaporate  a 
pound  of  water  supplied  at  155°  F.  into  steam  at  100  Ibs.,  gua^e- 
pressure,  requires  just  10  per  cent  more  heat  than  to  evaporate  a 
pound  of  water  supplied  at  212°  F.,  into  steam  at  ordinary  atmos- 
pheric pressure  at  the  sea-level,  or  "from  and  at  212°,"  a  term  fre- 
quently used  in  discussions  of  boiler-economy.  Eesults  of  boiler- tests 
are  commonly  reduced  from  the  figures  obtained  under  the  "actual 
conditions"  of  the  test  to  the  equivalent  evaporation  "from  and  at 
212°"  by  multiplying  these  figures  by  a  "factor  of  evaporation," 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.    191 

which  factor  may  be  found  by  calculation  from  the  formula  F  = 
(II  —  h)  -4-  965.7,  in  which  #and  li  are  respectively  the  heat-units  in 
1  Ib.  of  steam  of  the  given  pressure  and  in  1  Ib.  of  water  of  the  given 
temperature  found  in  the  tables  of  the  properties  of  steam  and  water, 
or  it  may  be  taken  directly  from  a  table  of  such  factors.  In  the 
present  case  the  "actual  conditions "  assumed  are:  Feed-water  155°  • 
steam-pressure  100  Ibs.  by  guage  (corresponding  to  a  temperature  of 
337°  F.),  and  factor  of  evaporation  1.10. 

Calculations  of  Fuel  Economy. — We  now  assume,  as  the  first  condi- 
tion which  governs  the  rate  of  driving  of  the  boiler,  that  the  coal  used 
is  of  a  fairly  good  quality,  equal  in  heating  value  to  an  ideal  perfectly 
dry  coal  containing  85  per  cent  of  pure  carbon  and  15  per  cent  ash. 

Let  us  also  assume  that  we  have  the  draft  of  the  boiler,  and  the 
thickness  of  the  bed  of  coal  on  the  grate,  so  regulated  that  enough  air 
is  supplied  to  burn  the  carbon  of  the  fuel  thoroughly,  forming  car- 
bonic acid  gas,  or  C02.  Each  pound  of  coal  burned  will  require 
about  20  Ibs.  of  air  to  burn  it,  including  enough  excess  of  air  to  insure 
that  no  portion  of  the  carbon  is  burned  imperfectly,  or  to  carbonic  ox- 
ide gas  (CO).  The  20  Ibs.  of  air  supplied  per  pound  of  coal  will 
measure  about  260  cubic  feet,  if  measured  at  a  temperature  of  60°  F. 

The  complete  combustion  of  a  pound  of  coal  will  generate  a  defi- 
nite quantity  of  heat,  which  may  be  calculated  and  expressed  in  "  heat- 
units,"  or  "British  thermal  units." 

The  quantity  of  heat  which  may  be  produced  by  the  complete  com- 
bustion of  1  Ib.  of  carbon  is,  approximately,  14,000  B.T.U. 

The  quantity  of  heat  required  to  evaporate  1  Ib.  of  water  from  a 
temperature  of  212°  into  steam  at  the  same  temperature,  or  from  and 
at  212°,  is  965.7  B.T.U. 

The  quantity  of  heat  required  to  evaporate  1  Ib.  of  water  supplied 
at  155°  into  steam  at  100  Ibs.  gauge-pressure,  is  10  per  cent  greater 
than  this,  or  1062  B.T.U. 

Dividing  14,600  by  965.7  we  obtain  15.21  Ibs.,  which  is  the  quan- 
tity of  water  which  may  be  evaporated  from  and  at  212°  by  the  com- 
plete combustion  of  1  Ib.  of  carbon,  on  the  supposition  that  all  the 
heat  generated  is  used  to  evaporate  the  water  and  none  is  allowed  to 
escape  by  radiation  or  in  the  gases  produced  by  the  combustion,  con- 
ditions which  are  ideal,  and  impossible  to  realize  in  practice. 

A  coal  whose  heating  value  per  pound  is  equal  to  85  per  cent  of 
that  of  pure  carbon,  is  theoretically  capable  of  producing  85  per  cent 


192  STEAM-BOILER  ECONOMY. 

of  this  result,  or  .85  X  15.21  =  12.93  Ibs.   evaporation,  from  and  at 
212°,  per  pound  of  coal. 

If  the  steam  is  generated  at  100  Ibs.  pressure  from  feed-water  at 
155°,  the  theoretically  possible  evaporation  is  -J-fJ  of  this,  or  12.93  -^ 
1.1  =  11.75  Ibs.  of  steam  per  pound  of  coal,  1.1  being  the  "factor 
of  evaporation/' 

This  is  the  maximum  amount  of  steam  which  it  is  possible,  theo- 
retically, to  produce  from  1  Ib.  of  coal  of  the  quality  assumed,  and 
under  the  conditions  given,  viz.,  feed-water  at  155°  and  steam -pressure 
100  Ibs.,  in  an  ideal  boiler,  in  which  there  is  no  waste  of  heat  by  radi- 
ation, by  escape  in  the  chimney  gases,  and  no  waste  of  coal  by  imper- 
fect combustion,  by  falling  through  the  grate-bars  or  by  removal  in 
the  ashes.  In  practice  all  these  wastes  occur,  and  the  percentage  of 
the  ideal  result  which  may  be  obtained  in  a  test  ranges  from  80,  under 
unusually  favorable  conditions,  down  to  50  or  even  less,  when  the  con- 
ditions are  unfavorable.  If  we  take  75  per  cent  as  the  highest  figure 
which  is  likely  to  be  reached  in  every-day  practice,  with  good  coal  and 
with  a  boiler  which  is  well  designed  and  driven  at  a  moderate  rate, 
then  we  may  expect  that  the  coal  of  the  quality  given,  with  feed-water 
at  155°  and  steam  at  100  Ibs.,  will  evaporate  11.75  X  .75  =  8.81  Ibs. 
as  a  maximum ;  and  if  the  boiler  is  not  properly  designed  for  the  service, 
or  is  driven  at  too  high  a  rate,  the  evaporation  per  pound  of  coal  may 
be  much  less  than  this  figure. 

Reversing  the  order  of  the  calculations  we  have : 

Actual  evaporation  per  Ib.  of  coal 8.81  Ibs. 

Equivalent  evaporation  from  and  at  212°,  8.82  X  1.1 9.69   " 

Equivalent  evaporation  per  Ib.  combustible,  9.69  -5-  85 11.40    " 

Efficiency,  11.40  -5-  15.21.. 75$ 

Boiler  Capacity  Depends  Upon  Economy. — The  discussion  thus  far 
has  apparently  made  a  wide  digression  from  the  problem  with  which  it 
started,  viz. :  how  much  steam  will  be  furnished  by  the  boiler  of  the 
form  and  size  selected.  The  complete  answer  to  the  problem,  how- 
ever, is  so  complicated  with  the  answer  to  the  other  question  of  how 
much  steam  may  be  generated  from  a  pound  of  coal,  that  it  seemed  ad- 
visable to  first  give  some  consideration  to  the  latter  question.  It  will  be 
seen  that  the  amount  of  steam  that  may  be  made  by  a  boiler  of  a  given 
size  depends  upon  the  amount  of  coal  which  may  be  burned  under  it, 
but  is  not  directly  proportional  to  the  amount  of  coal ;  and  the  amount 
of  steam  that  may  be  generated  by  the  combustion  of  a  pound  of  coal  • 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.    193 

depends  upon  the  boiler  and  upon  the  rate  at  which  the  boiler  is 
driven. 

Eeturning  now  to  our  cylindrical  boiler  30  ft.  long,  let  us  suppose 
that  its  length  is  divided  into  10  parts  or  sections,  of  which  the  first  two 
sections  are  directly  exposed  to  radiation  from  the  fire,  and  the  other- 
eight  receive  heat  by  conduction  from  the  heated  gases  in  their  pass- 
age to  the  chimney.  It  is  evident  that  the  first  and  second  sections 
will  each  transmit  a  greater  quantity  of  heat  into  the  water  than  the 
third,  that  the  third  will  transmit  more  than  the  fourth,  and  so  on. 
The  gases  will  gradually  diminish  in  temperature  as  they  travel  from 
the  furnace  to  the  chimney.  The  amount  of  heat  transmitted  to  the 
water  by  each  square  foot  of  heating  surface  in  a  given  time  will 
depend  upon  the  difference  between  the  temperature  of  the  heated 
gases  on  one  side  of  the  plate  and  that  of  the  water  on  the  other  side ; 
the  greater  this  difference  of  temperature  the  greater  the  heat  trans- 
mitted. Experiments  show  that  it  varies  about  as  the  square  of  that 
difference.  Thus  the  heat  transmitted  will  be  four  times  as  much  when 
the  difference  is  1000°  as  when  it  is  500°. 

Considering  then  that  our  boiler  is  divided  into  sections,  as  in  Fig. 
42,  and  that  a  fire  is  burning  on 
the  grate,  consuming  a  certain 
quantity  of  coal  per  hour,  and 
generating  a  temperature  which  FIG.  42. 

in  the  first  two  sections  averages  2600°  F.,  the  reduction  in  temperature 
may  be  considered  to  take  place  as  follows,  the  temperature  being 
taken  at  the  end  of  each  section : 

Section  No 2  3  4  56789          H 

Temperature  F 2200       1630      1290      1100      970      880      820      770       730 

Reduction 570        320        190      130        90        60        50        40 

The  reduction  of  the  temperature  of  the  consecutive  sections  is  a 
measure  of  the  quantity  of  heat  transmitted  by  each  section,  for  the 
quantity  of  heated  gas  remains  the  same,  and  the  quantity  of  heat  in  a 
given  quantity  of  gas  is  proportional  to  its  temperature. 

Suppose  now  we  increase  the  quantity  of  coal  burned  on  the  grate, 
so  that  a  greater  quantity  of  heated  gas  is  formed.  The  thickness  of 
the  bed  of  coal  being  increased  with  the  increase  of  draft,  so  that  the 
same  amount  of  air  is  used  per  pound  of  coal,  the  same  temperature  in 
the  furnace,  viz.,  2600°,  may  be  obtained;  but  the  temperatures  of  the 
sections  beyond  the  furnace  will  be  higher  than  before,  because  the- 


I7TTH 


194  STEAM-BOILER  ECONOMY. 

quantity  of  heated  gas  and  its  velocity  of  passage  toward  the  chimney 
are  both  increased,  and  the  capacity  of  a  square  foot  of  heating  sur- 
face to  absorb  heat  is  not  increased  by  the  increase  in  quantity  of  the 
gas  that  passes  under  it,  although  it  may  be  increased  by  the  increase 
of  the  difference  between  the  temperature  of  the  gas  and  that  of  the 
water  in  the  boiler.  The  reduction  in  temperature  of  the  gas  in  the 
consecutive  sections  may  now  be  as  follows : 

Section  No 2*3  4  5  6  7  8  9          10 

Temperature  F...  2300  1920  1670  1490  1360  1250  1160  1090  1030 
Reduction 380  250  180  130  110  90  70  60 

Comparing  these  two  statements  of  the  temperature  in  the  differ- 
ent sections,  we  note  several  things : 

1.  In  the  first  case  the  temperature  of  2600°  at  the  furnace  is  re- 
duced to  730°  at  the  chimney,  and  in  the  second  case  the  same  tem- 
perature at  the  furnace  is  reduced  only  to  1030°  at  the  chimney.     In 
the  first  case  the  temperature  at  the  chimney  indicates  a  loss  of  heat 
in  the  chimney  gases  of  730  -f-  2600  =  28  per  cent  of  the  heat  in  the 
furnace.     In  the  second  case  the  temperature  of  1030°  indicates  the 
loss  of  1030  -f-  2600  =  39.6  per  cent. 

2.  In  the  second  case  the  reduction  of  the  temperature  in  the  first 
three  sections  is  less  than  that  of  the  corresponding  section  in  the  first 
case.     This  does  not  mean  that  -the  heat  transmitted  is  less  in  the 
second  case  than  in  the  first,  for  the  quantity  of  gas  has  been  increased 
and  there  is  a  greater  quantity  of  heat  transmitted  while  the  reduction 
in  temperature  is  less. 

3.  In  each  section  in  the  second  case  the  temperature  is  greater 
than  in  the  corresponding  section  in  the  first  case.     The  difference 
between  the  temperature  of  the  gas  and  the  water  is  greater,  con- 
sequently the  transmission  of  heat  is  greater,  and  the  quantity  of 
steam  made  by  the  boiler  is  greater.     The  capacity  of  the  boiler  there- 
fore depends  to  a  considerable  extent  on  the  economy.     Increasing  the 
quantity  of  coal  burned  increases  the  capacity  while  it  reduces  the 
economy. 

4.  Although  in  the  second  case  a  greater  quantity  of  steam  is  made 
than  in  the  first,  it  is  not  made  with  the  same  economy  of  fuel,  for  the 
temperature  of  the  chimney  gases  is  greater,  showing  that  a  greater 
percentage  of  the  heat  generated  in  the  furnace  has  been  wasted. 

5.  Since  the  reduction  of  temperature  in  any  section  is  less  than 
that  in  the  preceding  section,  it  is  evident  that  in  the  first  case  an  ad- 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.   195 

dition  of  a  few  sections  to  the  length  cannot  add  much  to  the  economy 
of  fuel.  In  the  second  case,  however,  the  temperature  of  the  chimney 
gases  being  1030°,  it  is  evident  that  an  addition  of  several  sections  to 
the  length  might  be  made  before  the  gases  would  be  reduced  to  730°, 
the  temperature  of  the  chimney  gases  in  the  first  case.  It  is  also  evi- 
dent that  increasing  the  heating  surface  increases  both  the  capacity 
and  the  economy. 

Loss  of  Economy  Due  to  Insufficient  Heating  Surface. — What  has 
been  said  above  shows  the  necessity  of  proportioning  the  heating  sur- 
face to  the  amount  of  coal  to  be  burned,  rather  than  to  the  extent  of 
grate-surface;  and  so  proportioning  it  as  to  give  such  an  extent  of 
heating  surface  as  will  reduce  the  temperature  of  the  chimney  gases  to 
say  within  100°  or  200°  of  the  temperature  of  the  steam,  if  economy  of 
fuel  is  desired. 

Some  readers  may  think  that  all  this  is  so  very  simple  that  there 
should  be  no  need  of  explaining  it  at  so  great  length.  It  all  amounts 
to  the  simple  statement  that  economy  of  fuel  requires  that  the  tem- 
perature of  the  escaping  gases  should  be  low,  and  that,  to  secure  this 
low  temperature,  plenty  of  heating  surface  should  be  given.  This  is 
quite  true,  but  it  is  not  at  all  appreciated  by  many  boiler  users. 
Many  of  them  never  think  of  putting  a  pyrometer  or  a  thermometer 
in  the  stacks  of  their  boilers,  to  discover  by  that  means  whether  or  not 
there  is  a  waste  of  fuel.  They  are  quite  satisfied  if  their  boilers  give 
all  the  steam  that  is  required,  and  pay  little  attention  to  the  cost  of 
producing  that  steam.  It  has  therefore  seemed  desirable  that  this 
chapter  should  contain  not  only  the  simple  statement  above  given,  but 
also  in  considerable  detail  the  reasoning  upon  which  the  statement  is 
founded.  A  mathematical  treatment  of  the  subject  will  be  found  in 
the  chapter  on  " Efficiency  of  Heating  Surface." 

To  come  now  to  a  more  definite  statement  of  how  great  is  the  loss 
due  to  insufficient  heating  surface,  we  must  have  recourse  to  the 
records  of  experiments  upon  boilers. 

In  a  paper  on  "Efficiency  of  Boiler  Heating  Surface,"  by  Mr. 
11.  S.  Hale,  Trans.  Am.  Soc.  M.  E.,  vol.  xviii.,  he  gave  a  diagram 
showing  the  relation  of  the  evaporation  from  and  at  212°  per  pound  of 
combustible  to  the  evaporation  from  and  at  212°  per  square  foot  of 
heating  surface  per  hour,  as  obtained  by  plotting  the  results  of  tests 
with  anthracite  coal  given  in  Mr.  Geo.  H.  Barrus's  book  on  "  Boiler 
Tests."  This  diagram  is  here  reproduced,  Fig.  43.  The  small  circles 
represent  the  results  of  each  individual  test,  the  lower  curve  represents 


196 


STEAM-BOILER  ECONOMY. 


what  Mr.  Hale  considers  to  be  the  law  of  the  average  relation  between 
the  efficiency  and  the  rate  of  evaporation,  and  the  upper  line,  passing 

through  five  of  the  small  cir- 
cles, is  a  line  which  is  added 
to  represent  the  law  of  the  rela- 
tion as  derived  from  maximum 
results.  It  will  be  noticed  how 
very  far  below  the  maximum  are 
some  of  the  individual  results. 
Maximum  Possible  Econ- 
omy, —  On  another  diagram, 
Fig.  44,  is  plotted  together  with 


Lbs.  Wetter  Evaporated  per  )b.Combustib! 
<j>-*4coa}o:::rOo 

s> 

r 

\ 

^ 

ru, 

tf 

FT 

& 

^ 

>D 

/ 

i 

SO 

1 

^ 

i 

r>- 

ss 

\l 

^ 

j~ 

c 

-^ 

vif 

X 

^ 

Ny 

I 

- 

L 

n 

) 

N 

sx 

*s 

i 

\ 

5 

\, 

" 

\\ 

u 

f 

v 

\^ 

\, 

s. 

( 

— 

^x 

s 

n 

\ 

S 

F§x 

\      z     : 

5      4 

3         * 

) 

{ 

5      « 

1C 

Lbs  Evaporation  per  sq.ft.  Heatg  Surf.  perHour. 

FIG.  43. 


this     curve    of    Mr.     Barrus's 
maximum  results  another  curve 
representing  the  maximum  results  obtained  in  the  boiler  tests  made 


Lbs.  Evaporation  per  sq.  ft.    Heating  Surface  per  Hour. 

FIG.  44.— RELATION  OP  ECONOMY  TO  RATE  OF  DRIVING. 

at  the  Centennial  exhibition  in  1876.     The  particular  results  through 
which  the  curve  is  drawn  are  the  following: 


Name  of  Boiler. 

Lbs.  Water  Evaporated 
from  and  at  212°  per 
sq.  ft.  H.  S.  per  Hour. 

Lbs.  Water  Evaporated 
from  and  at  212°  per 
Ib.  Combustible. 

1.932 

11  938 

Root  

2.586 

12  094 

Smith  

3.739 

11.985 

GallowRy.   ...                    

5  413 

11  216 

Pierce  

6.698 

9  865 

The  smooth  curve  passes  directly  through  the  first  four  of  the 
above  results  and  a  little  above  the  fifth,  joining  the  curve  of  Mr. 
Barrus's  result  at  its  right-hand  extremity. 


ELEMENTARY  PRINCIPLES— TEE  PLAIN  CYLINDER  BOILER,    197 

As  the  Centennial  tests  were  made  under  exceptionally  favorable 
conditions,  and  as  the  maximum  results  of  these  tests  have  never  been 
surpassed  in  other  competitive  tests  with  anthracite  coal  in  which 
every  precaution  was  taken  by  impartial  observers  to  secure  accuracy, 
it  is  fair  to  consider  this  curve  as  representing  the  highest  possible 
evaporation  in  any  form  of  boiler  for  the  several  rates  of  evaporation 
per  square  foot  of  heating  surface  here  given.  Taking  approximate 
values  along  different  portions  of  the  curve  we  have  the  following: 

POUNDS   OP  WATER   EVAPORATED  FROM  AND  AT   212°. 

Per.  sq.  ft.  of  heating 

surface  per  hour. .     1.7      2      2.5      3         3.5      4  4.5      5         678 

Per  Ib.  of  combustible  11.9    13    12.1    12.1    12       11.85    11.7    11.5    10.8    9.8   8.5 

The  Centennial  tests  were  all  made  upon  other  forms  of  boiler  than 
the  plain  cylinder,  and  the  same  is  true  of  Mr.  Barrus's  tests.  There 
is  no  record  published  of  any  comprehensive  series  of  tests  upon  plain 
cylinder  boilers  from  which  we  might  draw  a  curve  expressing  the 
relation  of  the  efficiency  to  the  rate  of  evaporation,  but  we  may  make 
certain  reasonable  assumptions  concerning  them  which  may  enable 
us  to  draw  a  probable  curve. 

The  first  assumption  is  that  the  form  of  the  plain  cylindrical  boiler 
is  exceedingly  favorable  to  the  absorption  of  the  greatest  possible 
quantity  of  heat  by  every  square  foot  of  its  heating  surface.  The 
flames  and  heated  gases  travel  steadily  along  this  surface,  the  tendency 
of  heated  gases  always  to  ascend  tending  continually  to  keep  the 
hottest  portion  of  the  gas  in  contact  with  the  surface  above  it.  There 
is  no  shorter  path  by  which  the  gases  may  reach  the  chimney;  hence, 
there  is  no  tendency  to  short-circuiting  the  gases,  which  is  a  serious 
defect  in  many  other  forms  of  boiler.  The  thickness  of  the  metal  in 
the  shell,  rarely  more  than  J  inch,  is  not  so  great  as  to  cause  an  appre- 
ciably greater  resistance  to  the  passage  of  heat  through  it  than  that 
through  the  thin  tubes  of  tubular  boilers.  The  form  of  the  plain 
cylinder  boiler  seems,  therefore,  to  be  as  well  adapted  to  the  absorp- 
tion of  heat  as  that  of  any  other  boiler,  and  there  seems  to  be  every 
reason  to  believe  that,  as  far  as  the  absorption  of  heat  through  its 
shell  from  the  heated  gases  is  concerned,  it  should  be  quite  as  efficient 
as  the  best  of  the  boilers  tested  at  the  Centennial  exhibition,  and  that 
the  curve  expressing  its  maximum  results  would  follow  closely  the 
curve  of  maximum  results  of  the  Centennial  tests,  unless  there  is  some 
other  cause  not  yet  considered  which  would  prevent  it. 


198 


STEAM-BOILER  ECONOMY. 


Loss  of  Heat  by  Radiation. — There  is  such  a  cause,  and  that  brings 
us  to  the  second  assumption,  viz. :  that  the  radiation  loss  of  the  plain 
cylinder  boiler  is  very  much  greater  than  that  of  the  modern  types  of 
boiler  which  were  tested  at  the  Centennial  exhibition.  The  cylinder 
boiler,  30  ft.  long  and  30  in.  diameter  and  having  120  sq.  ft.  of  heat- 
ing surface,  will  have  approximately  120  sq.  ft.  in  the  upper  half  of  its 
shell  covered  with  a  non-conducting  covering,  more  or  less  imperfect, 
and  the  two  brick  side  walls  would  be  about  240  sq.  ft.  These  two 
side  walls,  however,  might  be  used  for  a  battery  of  three  or  four  boilers, 
as  in  Fig.  45.  A  return  tubular  boiler  of  double  the  diameter  and  half 
the  length  of  the  cylinder  boiler,  or  5  X  15  ft.,  would  have  only  about 


FIG   45. — BATTERY  OF  PLAIN  CYLINDER  BOILERS. 

80  sq.  ft.  of  the  upper  portion  of  its  shellc  overed  with  a  non-conductor, 
and  about  240  sq.  ft.  side  walls,  which  might  also  be  used  for  a  battery 
of  boilers.  But  the  tubular  boiler  might  have,  say,  60  4-in.  tubes  in- 
side of  it,  with  a  total  heating  surface  of  about  940  sq.  ft.,  which  are 
entirely  surrounded  by  water,  and  therefore  contribute  nothing  to  the 
loss  by  external  radiation.  The  total  heating  surface  of  the  tubular 
boiler  would  be  about  1100  sq.  ft.,  or  nine  times  as  great  as  that  of  the 
cylinder  boiler,  and  yet  would  expose  less  surface  to  external  radiation, 
so  that  the  loss  of  heat  by  radiation  from  the  cylinder  boiler  must  be 
much  greater  than  from  the  tubular  boiler.  How  much  greater  we 
have  no  means  of  knowing,  in  the  absence  of  direct  experiments.  Mr. 
Hale,  in  the  paper  before  mentioned,  in  discussing  tests  with  other 
boilers  than  plain  cylindrical,  says  that  the  radiation  in  some  of  these 
tests  could  not  have  been  over  2  per  cent  when  the  boilers  were  driven 
at  a  rate  of  evaporation  of  3  Ibs.  of  water  per  sq.  ft.  of  heating  surface 
per  hour,  and  that  "it  does  not  seem  possible  that  the  radiation  could 
in  modern  practice  have  gone  up  to  much  over  6  or  7  per  cent  at 
most,  and  it  is  probable  that  it  is  not  over  5  per  cent  if  it  is  as  much 
as  that."  The  "modern  practice"  referred  to  by  Mr.  Hale  is  not 
practice  with  plain  cylinder  boilers,  which  latter  may  be  called  ancient 
practice,  since  plain  cylinder  boilers  are  now  used  in  only  a  few  local- 
ities. We  will  probably  not  be  far  from  correct  if  we  assume  that  the 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.    199 

radiation  from  plain  cylinder  boilers  is  5  per  cent  greater  than  from 
the  boilers  tested  at  the  Centennial  exhibition,  when  the  calculation 
of  the  radiation  is  made  on  the  basis  of  the  rate  of  evaporation  being 
3  Ibs.  per  sq.  ft.  of  heating  surface  per  hour,  this  5  per  cent  being 
that  percentage  of  the  total  heating  value  of  the  pound  of  combustible. 
This  heating  value,  14,600  B.T.U.,  being  equal  to  an  evaporation  of 
15.2  Ibs.  of  water,  5  per  cent  of  this  is  0.76  lb.,  which  we  may  assume 
to  be  the  extra  loss  by  radiation  in  a  plain  cylinder  boiler  over  that  in 
a  modern  type  of  boiler  when  the  rate  of  evaporation  is  3  Ibs.  per  sq. 
ft.  of  heating  surface  per  hour.  When  the  rate  of  evaporation  is 
doubled  the  percentage  will  be  halved,  and  the  extra  loss  by  radiation 
will  then  be  0.38  lb.  If  the  rate  of  evaporation  is  less  than  3  Ibs.  the 
percentage  loss  will  be  greater.  Subtracting  the  extra  loss  as  cal- 
culated from  the  figures  already  given  as  taken  from  the  curve  of 
maximum  results  of  the  Centennial  tests  we  have  the  following: 


MAXIMUM    ECONOMY    OP    PLAIN    CYLINDER    BOILERS  :    POUNDS    WATER    EVAPOR- 
ATED  FROM   AND   AT   212°. 


Per  square  foot  heating  surface 
per  hour  

1  7 

3 

3  5 

4 

5 

6 

8 

Per   lb.   combustible,   max.    of 
other  boilers  Centennial  tests 
Subtract    extra    radiation    loss 
for  cylinder  boilers  .  .        ... 

11.90 
1  34 

12.05 
76 

12.00 
65 

11.85 
57 

11.50 
46 

10.85 
38 

8.50 

OQ 

Probable  maximum  perlb.  com- 
bustible, cylinder  boilers  

10.56 

11.29 

11.35 

11.28 

11.04 

10.47 

8.22 

The  figures  in  the  last  line  have  been  plotted  in  the  diagram,  Fig. 
44,  and  a  curve  drawn  through  them.  It  will  be  seen  that  the  maxi- 
mum economy  is  at  a  rate  of  combustion  .of  3.5  Ibs.  per  square  foot  of 
heating  surface,  that  below  this  rate  the  economy  is  decreased  on 
account  of  the  loss  by  radiation,  and  that  above  this  rate  the  economy 
falls,  at  first  slowly,  and  later  very  rapidly,  until  at  a  rate  of  evapora- 
tion of  8  Ibs.  per  square  foot  of  heating  surface  per  hour  the  evapora- 
tion is  only  8.22  Ibs.  per  lb.  of  combustible,  as  compared  with  the 
maximum  of  11.35  Ibs.  at  a  rate  of  3.5  Ibs. 

Beyond  the  rate  of  8  Ibs.  per  square  foot  we  have  no  experimental 
data  upon  which  to  base  conclusions.  If  the  direction  of  the  curve 
between  7  and  8  Ibs.  were  continued  in  a  straight  line,  as  the  shape  of 
the  curve  seems  to  indicate,  there  would  be  a  decrease  in  the  evapora- 
tion per  lb.  of  combustible  of  about  1.3  Ibs.  for  every  increase  of  1  lb. 


200 


STEAM-BOILER  ECONOMY. 


in  the  rate,  and  the  curve  would  cut  the  line  representing  0  Ibs.  evap- 
oration per  pound  combustible  at  a  rate  of  a  little  over  14  Ibs. 

Capacity  of  a  Plain  Cylinder  Boiler  at  Different  Rates  of  Driving, 
— We  now  have  the  data  from  which  to  calculate  the  probable 
amount  of  steam  that  will  be  made  by  the  plain  cylinder  boiler,  of  the 
size  selected,  at  different  rates  of  driving. 

PROBABLE    MAXIMUM   WORK   OF   A   PLAIN   CYLINDRICAL    BOILER     OF     120   SQ.    FT. 
HEATING    SURFACE   AND    12   SQ.    FT.    GRATE   SURFACE    AT    DIFFERENT     RATES    OF 

DRIVING. 


Rate  of  driving;  Ibs.  water  evaporated  per 
sq.  ft.  of  beating  surface  per  hour 

Total  water  evaporated  by  120  sq.  ft.  heat- 
ing surface,  per  hour,  Ibs 

Horse-power;  84.5  Ibs.  per  hour  =  1  H.P. 

?ounds  water  evaporated  per  pound  com- 
bustible      

Pounds  combustible  burned  per  hour 

Pounds  combustible  per  hour  per  sq.  ft. 
of  grate 

Pounds  combustible  per  hour  per  horse- 
power  


1.7 

204 
5.83 


10.5 
19.3 


1.61 
3.31 


860 
10.43 


5611 


.29 
31.9 

2.66 
306 


3.5 

420 
12.17 

11.35 
37.0 

3.08 
3.04 


480 
13.91 

11.28 
42,6 

3.55 
3.06 


6 

600     720 
17.3920.8727 


11.04 
54.3 

4.52 
3.12 


10.47 
68.8 

5.73 
3.30 


960 

.83 


8.22 
116.8 

9.73 
4.16 


From  the  figures  in  the  last  line  we  see  that  the  amount  of  fuel  re. 
quired  for  a  given  horse-power  is  nearly  37  per  cent  greater  when  the 
rate  of  evaporation  is  8  Ibs.  than  when  it  is  3.5  Ibs. 

The  figures  in  the  above  table  which  represent  the  economy  of  fuel, 
viz.,  "  Pounds  water  evaporated  per  pound  combustible,"  and  "  Pounds 
combustible  per  hour  per  horse-power,"  are  what  may  be  called 
4 'maximum"  results,  and  they  are  the  highest  that  are  likely  to  be 
obtained  with  anthracite  coal  with  the  most  skillful  firing  and  with 
every  other  condition  most  favorable.  Unfavorable  conditions,  such 
as  poor  firing,  scale  on  the  inside  of  the  heating  surface,  dust  or  soot 
on  the  outside,  imperfect  protection  of  the  top  of  the  boiler  from  ra- 
diation, leaks  of  air  through  the  brickwork,  or  leaks  of  water  through 
the  blow-oif  pipe,  may  greatly  reduce  these  figures. 

Disadvantages  of  the  Plain  Cylinder  Boiler. — An  inspection  of 
the  figures  will  reveal  one  of  the  reasons  why  in  most  parts  of  the 
world  the  plain  cylinder  boiler  is  no  longer  used.  The  boiler  we  have 
selected  for  illustration  is  of  quite  large  size,  30  feet  long,  2J  feet 
wide,  occupies  a  considerable  area  of  ground,  and  requires  quite  a 
costly  setting;  yet  when  driven  at  its  most  economical  rate,  it  develops 
only  12.17  H.P.,  or  when  driven  at  such  a  rate  that  its  fuel  consump- 
tion per  H.P.  is  37  per  cent  greater  than  at  its  most  economical  rate, 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.    201 

it  develops  only  27.83  H.P.  It  can  be  made  to  develop  a  still  greater 
horse-power,  but  only  by  a  much  greater  waste  of  fuel.  Where  fuel 
has  no  marketable  value,  such  as  sawdust  and  waste  lumber  at  saw- 
mills, refuse  coal  at  coal-mines,  and  the  like,  the  question  of  fuel 
economy  is  of  no  importance;  but  even  in  such  cases,  in  which,  say, 
1 0  or  more  pounds  of  water  may  be  evaporated  per  square  foot  of  heat- 
ing  surface  per  hour,  equal  to  35  H.P.  developed  by  a  boiler  of  120  sq. 
fi.  heating  surface,  it  is  probable  that  the  first  cost  of  the  plain 
•cylinder  boiler,  including  setting,  is  greater  than  that  of  some  more 
modern  form  of  boiler.  Where  refuse  coal  is  used  as  fuel,  the  cost  of 
hauling  it  and  the  cost  of  removal  of  ashes  should  be  considered,  and 
it  may  be  found  that  these  costs  alone,  even  when  fuel  costs  nothing, 
justify  the  use  of  a  boiler  which  economizes  fuel. 

Suppose  a  plant  of  boilers  at  a  coal-mine  is  used  to  generate  1000 
H.P.  of  steam.  Refuse  coal  is  used,  and  the  boilers  are  driven  at  such 
a  rate  that  4  tons  of  coal  are  used  for  every  3  tons  that  would  be  used 
by  boilers  driven  at  an  economical  rate.  It  requires  four  men  to 
handle  the  coal  and  ashes,  while  only  three  men  would  be  required 
with  the  economical  boiler-plant.  The  saving  of  one  man's  wages, 
say,  $450  per  year,  is  equal  to  5  per  cent  on  an  investment  of  89000, 
or  10  per  cent  on  an  investment  of  $4500.  So,  if  the  economical 
boiler-plant  of  1000  H.P.  did  not  cost  over  $4000  above  that  of  an  un- 
economical boiler-plant,  its  purchase  would  be  justified  from  a  finan- 
cial standpoint  even  in  a  case  where  fuel  costs  nothing. 

In  places  where  plain  cylinder  boilers  are  still  used,  two  points  are 
especially  claimed  in  their  favor:  First,  their  simplicity  of  construction, 
and,  second,  the  that  fact  they  are  easily  cleaned  from  scale  by  a  man 
getting  inside  of  them  with  hammer  and  chisel.  The  first  point  may 
be  admitted  without  question.  As  for  the  second,  it  may  be  said  that 
some  other  forms  of  boiler  are  kept  free  from  scale  as  easily  as  the 
cylinder  boiler,  and  that  it  is  generally  found  better  in  modern  prac- 
tice to  prevent  the  formation  of  scale  than  to  allow  it  to  form  and  then 
go  to  the  trouble  of  removing  it  by  hand  labor.  Whatever  may  be 
the  merits  of  the  plain  cylinder  boiler  in  regard  to  the  two  points 
mentioned,  they  are  more  than  offset  by  their  numerous  disadvantages. 

Besides  the  objections  to  the  plain  cylinder  boiler  already  spoken 
of,  viz.,  great  first  cost  when  driven  at  an  economical  rate,  great  waste 
of  fuel  when  forced  much  beyond  this  rate,  and  excessive  ground  space 
occupied,  there  are  others,  some  of  which  the  plain  cylinder  boiler 
holds  in  common  with  other  styles.  The  first  of  these  objections, 


202  STEAM-BOILER  ECONOMY. 

which  is  common  to  all  very  long  boilers,  is  the  difficulty  of  support- 
ing them  in  such  a  manner  that  excessive  strains  are  not  created  in 
the  sheets  and  rivets  by  the  weight  of  the  boiler  and  the  water  inside 
of  it,  in  addition  to  the  strain  due  to  the  pressure  of  steam.  When  a 
long  boiler  is  suspended  from  two  points,  whether  located  at  the  ends 
or  at  some  distance  from  them,  the  stresses  due  to  weight,  which  tend 
to  rupture  the  boiler  by  bending  it,  may  be  calculated;  but  when  sup- 
ported at  three  or  more  points  the  stresses  are  indeterminate — one 
support  may  sustain  much  more  weight  than  the  other — and  the  strain 
on  some  portion  of  the  shell  or  riveted  seams  may  be  greater  than  a 
proper  regard  for  safety  would  admit.  These  strains  are  apt  to  be 
changed  in  amount  or  in  direction,  as  from  tension  to  compression,  or 
vice  versa,  with  the  changes  in  temperature  in  boiler  and  setting  which 
take  place  when  the  boiler  is  put  into  or  out  of  service.  Even  if  the 
maximum  strains  due  to  the  weight  of  the  boiler  may  not  of  themselves 
be  sufficient  to  endanger  the  safety  of  the  boiler  when  new,  their  con- 
tinuance during  a  period  of  years  may  make  the  iron  hard  and  brittle, 
and  hence  give  rise  to  danger;  or  the  iron  may  in  time  become  weak- 
ened by  corrosion,  and  then  the  strains  caused  by  weight  of  the  boiler 
may  become  dangerous. 

Saving  Waste  Heat  of  the  Plain  Cylinder  Boiler. — The  chief  faults, 
of  the  plain  cylinder  boiler,  its  deficiency  of  heating  surface  and  high 
first  cost  compared  to  its  capacity  when  driven  at  anything  like  an 
economical  rate,  have  led,  as  already  stated,  to  its  general  abandon- 
ment wherever  the  cost  of  fuel  is  a  matter  of  importance.  In  some  old 
plants,  however,  where  cylindrical  boilers  are  already  in  use,  and 
when  they  are  still  in  good  condition  to  furnish  steam  of  the  pressure 
desired,  but  are  driven  at  such  a  rate  as  to  be  wasteful  in  fuel,  it  has 
been  found  economical,  instead  of  replacing  the  old  boilers  with  new 
ones,  to  add  to  them  an  "economizer"  in  which  a  large  part  of  the 
waste  heat  may  be  saved. 

Use  of  a  Water-tube  Boiler  as  an  Addition  to  a  Cylinder  Boiler.— 
Sometimes  it  is  found  that  the  waste  gases  from  a  cylinder  boiler 
are  so  high  in  temperature  that  they  may  be  advantageously  utilized 
by  passing  them  into  another  boiler.  Several  of  the  modern  forms  of 
water-tube  boiler  may  thus  be  used.  An  instance  of  the  kind  is  de- 
scribed in  a  catalogue  (1897)  of  the  Morrin  "  Climax"  boiler.  The 
gases  escaping  from  a  plant  of  twelve  cylinder  boilers  30  ft.  long,  30 
ins.  diameter,  located  at  No.  2  shaft  at  Nanticoke,  Pa.,  ranged  from 
1500°  F.  with  the  blowers  off  to  2000°  with  the  blowers  on.  A  400- 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER,    203 

H.P.  Climax  boiler,  26£  ft.  high,  11  ft.  2  ins.  diameter,  containing 
3940  sq.  ft.  of  heating  surface,  was  placed  between  the  two  stacks 
that  carried  off  the  waste  gases  from  the  twelve  boilers.  Two  brick 
flues  conducted  the  gases  to  the  Climax  boiler,  the  outlet  to  the  old 
stack  being  cut  off  by  iron  doors.  A  test  made  when  No.  2  buckwheat 
coal  was  used  under  the  cylinder  boilers  showed  that  the  Climax  boiler, 
driven  by  the  waste  gases  alone,  developed  526.7  II. P.,  or  over  30  per 
cent  more  than  its  own  rating.  The  temperature  of  the  gases  after 
they  had  passed  through  the  Climax  boiler  was  520°.  It  is  stated  con- 
cerning this  result  that  when  cylinder  boilers  are  used  it  is  possible  to 
double  their  capacity  without  using  an  ounce  more  coal,  or  employing 
another  hand.  This  would  be  possible  only,  of  course,  when  the  tem- 
perature of  the  gases  leaving  the  cylinder  boilers  is  very  high,  say 
1500°  F.  or  over. 

At  one  of  the  Philadelphia  &  Reading  collieries,  one  250  H.P.  Cahall 
vertical  boiler  was  placed  at  the  rear  of  twelve  plain  cylinder  boilers 
of  the  ordinary  dimensions  common  in  anthracite  colliery  practice.  A 
simultaneous  test  was  made,  in  1896,  by  J.  M.  Whitham,  of  the  per- 
formance of  the  cylinder  boilers  and  the  Cahall  boiler.  Mr.  Whitham 
summarized  his  results  as  follows: 

1.  The  cylinder  boilers  are  run  to  develop  from  33  to  35  H.P. 
each. 

2.  The  cylinder  boilers  by  themselves  evaporate  3.77  Ibs.  of  water 
from  and  at  212°  per  Ib.  of  dry  coal. 

3.  The  combination  of  cylinder  boilers  and  Cahall  boilers,  the  lat- 
ter using  waste  heat  only,  permits  an  evaporation  of  6.98  Ibs.  of  water 
from  and  at  212°  per  Ib.  of  dry  coal. 

4.  The  waste  gases  enter  the  Cahall  setting  at  about  1600°  F., 
and  leave  it  about  700°. 

5.  The  use  of  waste  gases  by  the  Cahall  boiler  increases  .the  available 
horse-power  of  the  plant  from  74  to  85  per  cent,  according  to  the  num- 
ber of  boilers  used  for  supplying  the  waste  heat. 

6.  The  250-H.  P.  Cahall  boiler  using  waste  gases  from  eight  cylin- 
der boilers  developed  207.6  boiler  H.P.,  and  when  supplied  by  twelve 
boilers,  it  developed  334.1  H.P.,  or  33.6$  above  its  rating. 

7.  The  fuel  used,  called  a  "rice  mixture,"  consisted  of  20$  slate 
pickings,  8$  buckwheat,  46$  rice-coal,  and  26$  dirt.     It  contains, 
as  used  at  this  colliery,  from  6.25  to  9.5  per  cent  moisture,  and  from 
32.4  to  34  per  cent  ash  and  refuse.     It  is  burned  with  a  strong  fan- 
blast. 


204  STEAM-BOILER  ECONOMY. 

Modern  Boiler  Practice  in  the  Anthracite  Coal  Regions. — In  the 

anthracite  coal  regions  plain  cylinder  boilers  are  still  (1901)  used  in 
the  majority  of  mining  plants,  but  as  they  become  worn  out  they 
are  being  replaced  by  other  styles.  The  common  horizontal  return 
tubular  boiler  has  been  largely  adopted,  chiefly,  no  doubt,  on  account 
of  its  low  first  cost,  while  of  the  water-tube  boilers,  the  Babcock  & 
Wilcox,  the  National,  the  Cahall,  the  Stirling,  and  the  Climax  are  all 
represented. 


CHAPTER  IX. 

EFFICIENCY   OF  THE   HEATING  SURFACE. 

ASSUMING  that  the  fuel  is  burned  completely  in  the  furnace,  gen- 
erating a  quantity  of  hot  gas,  which  contains  all  the  heat  produced 
by  the  combustion,  we  now  have  to  consider  what  proportion  of  this 
heat  is  absorbed  by  being  transmitted  through  the  metal  beating  sur- 
face of  the  boiler  into  the  water;  in  other  words,  what  is  the  effi- 
ciency of  the  heating  surface.  This  will  depend  not  only  on  the  na- 
ture, extent,  and  arrangement  of  the  heating  surface,  that  is,  on  the 
boiler  itself,  but  also  on  the  rate  at  which  it  is  driven,  and  on  other 
conditions  of  its  operation.  A  theoretical  discussion  of  the  subject 
will  first  be  given,  and  then  the  relation  of  the  theory  to  practice  will 
be  shown. 

NOTATION. 

S  =  area  of  heating  surface  in  sq.  ft. 

W=  actual  water  evaporated,  Ibs.   per  hour,  reduced  to  equivalent 

evaporation  from  and  at  212°,  or  U.E.*  per  hour. 
W'-=  same  when  radiation  is  so  small  that  it  may  be  neglected,  or 

W  +  radiation,  in  U.E.  per  hour. 
K  —  heating  value  of  the  fuel  in  B.T.TJ.  per  Ib. 
F  =  fuel  used,  Ibs.  per  hour. 
f    —  weight  of  gases  per  Ib.  of  fuel. 
w  =  Ff,  =  weight  of  dry  gases,  Ibs.  per  hour. 
c    =  specific  heat  of  gas,  considered  as  a  constant. 
t    =  excess  of  the  temperature  of  the  water  in  the  boiler  above  the 

atmospheric  temperature. 
T  =  temperature  (above  atmosphere)  of  the  gas  in  contact  with  some 

given  portion  of  the  heating  surface. 
TI  ,  T2  =  initial  and  final  values  of  T. 

*  U.E.  =  units  of  evaporatioH. 

205 


206  STEAM-BOILER  ECONOMY. 


i  —  total  heat  supplied  to  the  gas  by  the  burning  of  the  fuel,  on 
the  supposition  that  all  of  the  heat  generated  is  first  utilized 
in  raising  the  temperature  of  the  gas  before  it  comes  in 
contact  with  the  heating  surface. 
ctvT2  =  heat  lost  in  the  gases  escaping  to  the  chimney. 
a    =  a  coefficient  of  resistance  to  transmission  of  heat,  and  of  other 

elements  of  inefficiency,  more  fully  explained  later. 
Ep  =  possible  evaporation,  in  IT.  E.  per  Ib.  of  fuel  if  all  the  heating 

value  of  the  fuel  were  utilized. 
Ea  =  actual  evaporation,  in  U.E.  per  Ib.  of  fuel. 
j&V—  same  when  radiation  is  not  taken  into  account,  or  Ea  -f-  radia- 

tion, in  U.E.  per  Ib.  of  fuel. 
R  =  radiation  in  U.E.  per  sq.  ft.  of  heating  surface  per  hour. 

In  what  follows  we  shall  at  first  consider  the  radiation  so  small 
that  it  may  be  neglected. 

TH~?  .  .  ,,     ,      ,  .  ,.          Ea      cw(T  \  —  T^)      T,  —  T«       .  ,. 

Efficiency  of  the  heating  surface  =  -=-  =  —  -  —  ^  —  •  -  =  -J-~  —  2  .      (1) 

This  fraction  is  the  ratio  of  the  heat  absorbed  by  the  boiler  to  the  heat 

supplied  by  the  fuel.* 

q-=  rate  of  conduction  in  U.E.  per  hour  per  sq.  ft.  of  heating  surface, 

corresponding  to  any  difference  of  temperature  T—  t  of  the 

gas  and  of  the  water. 
qdS  =  heat  transmitted  per  hour  through  any  small  portion  dS  of  the 

heating  surface. 
cwd  T  =  heat  lost  by  the  gas  in  passing  over  the  portion  of  heating 

surface  dS\  qdS  —  cwdT. 

After  the  hot  gas  passes  over  the  elementary  portion  dS  of  the 
heating  surface,  losing  the  temperature  dT,  it  arrives  at  the  next  equal 
elementary  portion  with  a  diminished  temperature,  and  transmits  heat 
through  it  at  a  diminished  rate,  since  the  rate  of  conduction  q  de- 
creases in  some  ratio  with  the  decrease  of  the  difference  of  temperature 
T  —  £;  and  so  on,  transmitting  a  less  and  less  quantity  through  each 
successive  equal  portion  of  surface,  until  it  finally  leaves  the  heating 
surface  at  the  temperature  T2. 

m    _  rn 

*Rankine  uses  a  different  expression    for  efficiency,  viz.,  —  -  -  ?,    or  the 

ratio  of  the  heat  absorbed  to  the  heat  which  would  be  absorbed  if  the  gases  were 
cooled  down  to  the  temperature  of  the  water  in  the  boiler.  This  is  not  as  con- 
venient as  the  expression  used  above,  and  it  is  not  in  harmony  with  the  usual  defi- 
nition of  efficiency,  viz.,  energy  utilized  -j-  energy  supplied. 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


207 


For  the  whole  heating  surface  S,  and  the  corresponding  decrease 
of  temperature  of  the  hot  gas  from  T^  to  T2,  we  have  the  integral  of 
the  above  differential  expression : 


-T2)=  J 


qd8, 


or 


CIO 


The  second  member  of  this  last  equation  may  be  integrated  when  we 

find  the  law  of  the  relation  of  q  to  T  —  t. 

Rankine  represents  these  principles  graphically  as  follows : 

Draw  AD,  Fig.  46,  to  represent  the  whole  heating  surface  S,  and  let 

any  portion  of  that  line,  as  AX,  represent  5,  a  part  of  that  surface. 

Let  AB  —  ql ,  the  rate  of  conduction  for  the 

initial   temperature    Tr     In  DA   produced,    r          n 

take  AO  =  ~    — -;  then  the  rectangle 

(h 

OABCwill  equal  the  whole  heat  of  the  hot 
gas  proceeding  from  the  furnace  per  hour, 
measured  above  the  temperature  t ;  for 


AO  X  AB  =  AO  X  q,  ~  cw(T^  -  t).  u  j  f 

FIG.  46. 
Let  XY  =  q  =    the  rate  of  conduction 

corresponding  to  the  temperature  of  the  gas  after  having  passed  over 
the  portion  AX  of  the  heating  surface,  and  let  BYE  be  a  curve  drawn 
through  the  summits  of  a  series  of  such  ordinates;  then  the  area  of  any 
part  of  that  curve,  such  as  ABYX,  represents  the  heat  transferred  per 
hour  through  the  part  AX  of  the  heating  surface;  and  the  area  ABED 
the  heat  transferred  through  the  whole  surface  AD:,  and  when  the 
curve  BYE  is  produced  indefinitely,  the  area  contained  between  it  and 
its  asymptote,  AD  produced,  approximates  indefinitely  to  that  of  the 
rectangle  OABC. 

The  definite  results  of  these  principles  depend  on  the  relation  be- 
tween q  and  Tr 

For  small  differences  of  temperature  it  is  found  experimentally 
that  the  rate  of  transmission  of  heat  through  metal  plates  is  nearly 
proportional  to  the  difference  of  temperature  of  the  fluids  on  the  two 
sides  of  the  plate,  but  for  great  differences  of  temperature,  such  as 


208  STEAM-BOILER  ECONOMY. 

those  existing  in  steam-boiler  furnaces,  the  transmission  increases  at  a. 
faster  rate  than  the  difference  of  temperature,  so  that  it  is  nearly  pro- 
portional to  the  square  of  the  difference,  as  is  shown  by  Blechynden's 

(Jl  _   A2 

experiments,  which  will  be  described  later.    Rankine  gives  q  =  -  —  —  -, 

ct/ 

in  which  a  is  a  coefficient  whose  value  may  be  determined  by  experiment, 
and  he  gives  its  value  as  from  160  to  200.  The  method  of  deducing 
the  value  of  a  from  data  of  experiments  on  steam-boilers  will  be  given 
later  ;  and  it  will  also  be  shown  that  it  is  a  function  of  other  things 
besides  the  resistance  of  the  metal  to  the  transmission  of  heat. 
Using  this  value  of  q  we  have 


Whence  * 


.          _  _ 

cwa  ~  T,  -  t  ~  T,  -  t  ~  (T2  -  t)(T,  -  t)'  ' 

By  combining  equations  (1)  and  (4)  we  may  obtain 


,_  i_ 

in   which  equation  Tt  has  disappeared.      (Appendix,  note  2.)     Let 

^^•=B,  saA  •=?£-.=  A;  ac/=(Tl-t)A.     Then  (5)  becomes 
*i  Ji~  t 

B 


Hence  Ea'=BEp-~~, (7) 

w 

which  is  the  equation  of  a  straight  line  if  EJ  and  -^  are  variables.  It 
shows  that  the  evaporation  per  pound  of  fuel  is  a  function  of  the  rate 

*  See  note  1,  appendix  to  this  chapter. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  209 

of  evaporation  per  square  foot  of  heating  surface,  and  is  affected  by 
two  coefficients,  A  and  B. 

J9,  being  a  function  of  the  initial  temperature  of  the  gas  Tl ,  de- 
pends on  the  heating  value  of  the  fuel  and  on  the  volume  of  gas,  that 
is,  on  the  air-supply.  Let  K  =  heat-units  per  Ib.  of  fuel  burned, 
=  TJc.  Then 


r. 


(8) 


and 


acf 


expressions  from  which  we  may  find  the  value  of  A  and  B  when  the 
heating  value  of  the  coal,  the  temperature  of  the  water  in  the  boiler, 
the  weight  of  gas  per  Ib.  of  fuel,  and  the  specific  heat  of  the  gas  are 
known.  The  value  of  A,  however,  depends  upon  that  of  the  experi- 
mental coefficient  «.* 


Values  of  the  Coefficients  B  and  A. 

If  in  the  equations  B  =  -     -^  ^  and  A  =  •     °^       we  substitute 

assumed  numerical  values  as  follows:  K=  13,000,  14,000,  and  15,000; 
t  =  250  and  300;  c  =  Q.24;  /  =  20,  30,  and  40;  a  =  200,  300,  and 
400,  we  obtain  values  of  B  and  A  as  follows : 


K-  tcf 


V  UbUVS 

For/  - 

K 

250°        250° 

250° 

300° 

300° 

300° 

/  = 

20           30 

40 

20 

30 

40 

ForJT=  13,000,  B  = 

.91          .86 

.82 

.89 

.83 

.78 

=  14,000,  B  = 

.91          .87 

.83 

.90 

.85 

.79 

=  15,000,  B  = 

.92          .88 

.84 

.90 

.86 

.81 

*Up  to  this  point  the  treatment  of  this  subject  is  based  partly  on  that  of 
Rankine  ("  Steam-engine,"  p.  262)  and  partly  on  that  of  Ha^e  (Trans.  A.  S.  M.  E., 
vol.  xviii.  p.  330).  What  follows  is  original  work  of  the  author. 


210 


STEAM-BOILER  ECONOMY. 


K  CM-  tiCS 

For*  = 

vj  -a.  : 
250° 

250° 

250° 

300° 

300° 

300° 

f  = 

20 

30 

40 

20 

30 

40 

For  K  =  13,000, 

a  =200, 

A  = 

.39 

. 

92 

1.74 

.40 

.95 

1.82 

=  300, 

A  = 

^59 

1. 

39 

2.61 

.60 

i 

.43 

2.73 

=  400, 

A  = 

.78 

1. 

85 

3.48 

.80 

i 

.91 

3.64 

For  K  =  14,000, 

a  =  200, 

A  = 

.36 

, 

85 

1.59 

.37 

.87 

1.66 

=  300, 

A  — 

.54 

1. 

27 

2.38 

.55 

i 

.31 

2.48 

=  400, 

A  — 

.72 

1. 

70 

3.18 

.73 

i 

.75 

3.31 

For  K  =  15,000, 

a  =  200, 

A  = 

.33 

. 

79 

1.46 

.34 

.81 

1.52 

=  300, 

A  = 

.50 

1. 

18 

2.19 

.51 

i 

.21 

2.28 

=  400, 

A  = 

.67 

1. 

57 

2.93 

.68 

i 

.61 

3.04 

Graphical  Interpretation  of  Formula  (7). — On  a  system  of  rectan« 

Wf 

gular  co-ordinates,  Fig.  47,  lay  out  Ep  and  BEf  as  ordinates  and  -~- 

as  abscissa.     From  the  end  of  the  ordinate  BEp 
draw  a  straight  line  inclining  downwards  at  an      "7^~ 
angle  whose  tangent  is  A.    Then  for  any  value 

W 

of  the  abscissa  -~-  the  corresponding  value  of 

Ea'  will  be  the  length  of  the  ordinate  drawn 

W 

from  the  extremity  of  -~-  to  the  inclined  line. 


The  inclined  line  can  never  reach  the  axis  of 


FIG.  47. 


abscissas,  and  the  rate  of  evaporation  -=-   can  never  be  as  great  as 
-,—  .     (Appendix,  note  3.) 

A 

Radiation  Considered. — In  the  above  formulas  no  account  has  been 
taken  of  radiation  into  the  atmosphere  from  the  external  walls  of  the 
boiler  and  furnace.  For  a  given  value  of  F  and  S  radiation  will  tend 
to  reduce  the  values  of  Ea'  and  W.  Let  r=  radiation  expressed  in  units 
of  evaporation  per  Ib.  of  fuel,  then  total  radiation  per  hour  =  rF9  and 

rF 

radiation  in  U.E.  per  hour  per  sq.  ft.  of  heating  surface  =  -~-  =  R. 

Ea'  =  Ea  -f-  r.         W '  =  W  H 
-  Formula  (7)  then  becomes 


E  = 


.    .    (10) 


For  a  given  temperature  t  of  the  water  in  the  boiler  and  ordinary 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


211 


furnace  conditions,  rF  and  R  will  be  practically  constant.  They  will 
represent  but  a  small  percentage  of  the  heat  generated  in  the  furnace 
when  the  rate  of  driving  is  high,  and  a  large  percentage  when  the 
rate  becomes  very  low. 

Graphical  Representation  of  Formula  (10). — Formula  (10)  may  be 

expressed  Ea  =  BEP  —  A-^  —  AR  —  r, 

and  it  may  be  represented  graphically 
as  in  Fig.  48,  the  height  Ea  of  any 
point  of  the  curved  line  above  the  base 
line  representing  the  actual  evaporation 
corresponding  to  a  certain  rate  of  evap- 
oration W/S.  In  the  equation  there  are 
three  quantities  which  are  subtracted 
from  BEp,  and  these  are  shown  on  the  dia- 
gram :  Afi,ii  constant;  A  W/S,  which  in- 
creases directly  as  W/S\  and  r  =  RS/F, 
which  increases  rapidly  as  W/S  approaches  0.  When  W/S  and 
Ea  =  0,  r  =  BEP  -  AR. 

Efficiency  when  Radiation  is  Considered. — We  have 


CO 


FIG.  48. 


RS 


since     R  =  ~     and     F  —  -JT-  • 
o  J^a 


Substituting  this  value  of  r  in  eq.  (10)  it  becomes 


E,  =  BE,  -  A 


(See  Note  4,  Appendix.) 


R8Ea 
W 


Efficiency  =  ~-  = 

-£-/p 


RS 


rfV'T-  •   <«) 

+  W 


-^- (13) 


An  Arithmetical  Example. — Consider  first  the  case  in  which  ra- 
diation is  so  small  that  it  may  be  neglected.     We  will  suppose  the  fol- 
lowing data  to  have  been  obtained  in  a  test  of  a  boiler,  and  assume  that 
all  the  fuel  is  completely  burned,  the  whole  of  the  heat  generated 
being  first  applied  to  raising  the  temperature  of  the  gases  of  combus- 
tion before  they  come  in  contact  with  the  heating  surface: 
Heating  value  of  the  fuel  =  K=  13,570  B.T.U.   per  Ib. ; 
Ep  =  13,570  -T-  965.7  =  14.05  U.E.  per  Ib.  of  fuel, 


212  STEAM-BOILER  ECONOMY. 

S  =  1000  sq.  ft.  ;  F  =  300  Ibs.  per  hour; 

W=  75^  of  14.05  X  jF=10.538  X  300  =  3161  Ibs.  per  hour; 
/  =  24  Ibs.  gas  per  Ib.  fuel;  c  —  0.24,  specific  heat; 

w  =  Ff  =  7200  Ibs.  gas  per  hour. 

K      13  570 

TI  =  -f-  =      *        =  2356°  elevation  above  atmospheric  temperature; 
c         y«  i  o 


l2  =  75#  efficiency;  T2  =  25$  of  2356  =  589°; 

A 

t  =  temperature  of  water  —  atmospheric  temperature, 

=  341°  F.  —  60°  =  281°; 
1—  r2  =  1767°;         7;—*  =  2075°;         T2-t 


We  now  have  all  the  values  required  for  substitution  in  formula  (4) 
except  a. 

Formula  (4)  is 

_S_          1  1  TI  -  T, 

cwa~~  Tt-t      i;  -  t  "  (Tn  ~  t)  (T,  -  ty 

Substituting  the  values,  we  have 

1000  1  1  1767 


0.24  X  7200  X  a      308      2075      308  XU2075* 
Whence  a  =  209.3. 

W 

Take  now  formula  (7),     Ea'  =  BEP  -  A  --. 


acf     _  209.3  X  0.24  X  24  _ 
-  TI  _  t  ~  2075 

*  /<*    R      -g-fo/      13,570  -  281  X  0.24  X  24  _ 

or,  from  eq.  (8),  B=  —  -^  13^57Q  -  =  0.880i  ; 

0c'/3         209.3  X  0.24'  X  242 
and  eq.  (9),        A  =  g—^=       13,570  -  1619  °'581' 


EFFICIENCY  OF  THE  HEATING  SURFACE.  213 

W 


a'  =  BEP  -A  -^-=  0.8807  X  14.05  -  0.581  ~  =  10.538. 


1UUU 


Ea'      10.538 

Ef  =  =  1^05-  -^  efficiency. 


2.  We  will  now  assume  that  radiation  from  the  boiler  and  furnace 
amounts  to  2$  of  the  heating  value  of  the  fuel,  reducing  the  efficiency 
to  73^  instead  of  75. 


20  of  Ep  =  14,05  X  .02  =  0.281  =  r. 
_  rF_  0.281  X  300 

=  ti  z        1000 

=  0.0843  U.E.  per  hour  per  sq.  ft.  of  heating  surface. 
W=W  —  RS=  3161  -  84  =  3077. 

BEP          .W     0.8807X14.05  D1 

Formula  (11),    Ea=-   --A-  =  -  --  0.581 


. 

"If  "^3077 

=  10.256  U.E.  per  Ib.  fuel. 


Formula  (12),  Efficiency,  ^  =  -  -?-^-  -  — 


0.8807         0.581  x  3077 

=  U.  7o. 


84.3        1000  X  14.05 

^3077" 

NOTE. — If  the  fuel  contains  hydrogen  and  water,  the  values  of  B 

and  A  should  be  obtained  respectively  from  — 4= —   and  -=— -—   and 

J.  J.  j  —  t 

not  from  eqs.  (8)  and  (9),  since  the  value  of  K  in  these  equations, 
determined  from  the  analysis,  is  the  total  heating  value,  the  water  in 
products  of  combustion  being  condensed  and  cooled  to  the  atmospheric 
temperature.  If  the  "  available "  heating  value  is  used  as  the  value 
of  K,  this  should  be  computed  on  the  basis  of  the  superheated  steam 
escaping  from  the  furnace  at  the  temperature  of  the  furnace.  It  may 
be  obtained  more  directly  from  the  formula  K '=  T^fc,  Tl  being  cal- 
culated from  the  formula  given  on  page  29,  viz. : 

_  6160  4-  2220H  -  3270  -  44  water 
/+  0.02  water  -  0.18H 


214  STEAM-BOILER  ECONOMY. 

Example  2.  —  Kequired  the  efficiency  of  a  boiler  using  moist  wood  as 
fuel,  the  wood  having  the  composition  given  on  pages  25  and  29,  with  K 

=  6168  B.T.U.,  /  =  15,  Tv  =  1403°,  a  =  200,  •—=  3,  R  =  0.081, 
t  =  300. 


If 

=  6168  -T-  965.7  =  6.387  U.E. 
T-  t       1403  -  300 


_  200  X  0.24  X  15 
-  V=l~  1103 

Efficiency  =  §L  =  _^^L.  -0.653  X  ^  =0.765-0.307=0.458. 
•~p       -i        U.Uol  b.oy 

~~3~ 

Ea  =  0.458  X  6.39  =  2.926   Ib.   evaporated  from  and 
at  212°  per  Ib.  of  wood. 

Or,  from  formula  (12),  Ea  =  —  :  '—?-„  --  ^- 


This  example  shows  what  very  low  efficiency  may  be  obtained 
from  moist  fuels  when  the  air-supply  is  excessive,  even  at  moderate 
rates  of  driving.* 

Example  8.  Other  conditions  being  the  same  as  above,  let  /  =  10 
and  T,  =  2020. 

T  —  t      1720 


a'-f        200  X  0.34  X  10  _     970 
'-  77=1  -          T720~ 

rr  r\  OKI  q 

Efficiency  =  ^  =  ^  -  0.279  x  ^  =  0.698. 

Ea  =  0.698  X  6.39  =  4.46  Ibs.  evaporation. 

*  The  air-supply  for  maximum  economy  is  about  50$  in  excess  of  that  required 
to  burn  the  C  to  CO2  and  the  H  to  H2O,  in  order  to  insure  that  all  the  C  is  burned 
to  CO2  and  none  to  CO.  This  corresponds  to  about  18  Ibs.  of  air  per  Ib.  of  com- 
bustible for  anthracite  and  semi-bituminous  coal,  but  to  a  much  smaller  quantity 
for  fuels  high  in  oxygen  and  moisture,  say  9  to  12  Ibs.  for  wood  and  lignite. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  215 

Calculation  of  the  Values  of  A,  B,  and  a  from  the  Results  of  Boiler 
Trials. — From  the  report  of  the  boiler  trials  at  the  Philadelphia  Ex- 
hibition in  1876  we  obtain  the  following  data  of  the  trials  of  the  six 
boilers  showing  the  highest  results  reached  in  the  economy  trials  with 
anthracite  coal,  together  with  the  similar  data  of  the  capacity  trials  of 
the  same  boilers: 

Economy  Trials.  Capacity  Trials. 

E  W  S  E  W  S 

*"  IT  ~w  a  ~s~  W 

Root 12.094  2.586  .337  10.441  3.207  .312 

Firmenich 11.988  1.932  .518  11.064  2.287  .437 

Lowe 11.923  2.149  .466  11.163  3.171  .315 

Smith 11.906  2.785  .359  11.925  3.739  .267 

Babcock  &  Wilcox..  11.822  2.791  .358  10.330  3.840  .260 

Galloway 11.583  4.178  .239  11.216  5.413  .185 

Ea  =  Ibs.  of  water  evaporated  from  and  at  212°  per  Ib.  of  combustible;  W/S  = 
U.E.  per  sq.  ft.  of  beating  surface  per  hour. 

Many  desirable  data  are  lacking  in  the  report  of  these  trials,  such 
as  analyses  of  the  fuel  and  of  the  chimney-gases,  the  temperature 
of  the  fire,  the  weight  of  the  gases  per  pound  of  combustible,  which 
might  be  calculated  from  the  analyses,  and  an  estimate  of  the  loss  by 
radiation.  From  the  information  available,  however,  reasonable 
assumptions  may  be  made  of  the  data  that  are  lacking. 

The  coal  was  selected  anthracite,  and  its  heating  value  per  Ik  was 
probably  not  far  from  14,800  B.T.U.  per  Ib.  of  combustible.  We 
take  then  K—  14,800,  and  'Ep  =  JT-r-  965.7  =  15.325. 

We  may  assume  that  the  radiation  per  Ib.  of  fuel  was  equal  to  3#  of 
Ep  when  the  boilers  were  driven  at  the  average  rate,  corresponding  to 
a  fuel  consumption  of  0.231  Ib.  of  combustible  per  sq.  ft.  of  heating 
surface.  We  have  then 

r  =  0.03  X  15.325  =  0.46,     and     R  =  r-^  =  0.106, 

or,  say,  R  —  0. 1 

From  the  fact  that  the  economy  tests  gave  very  high  figures,  it  is 
not  probable  that  the  weight  of  gases  per  Ib.  of  combustible  greatly  ex- 
ceeded 20  Ibs. ;  but  we  shall  make  two  separate  assumptions,  for  the  pur- 
pose of  illustration,  viz.,  that/  —  20  and  30  Ibs.,  and  make  the  calcula- 
tions on  both  assumptions.  The  temperature  of  the  steam  due  to  the 
pressure  used  in  the  trials  was  about  316°,  and  taking  the  tempera- 
ture of  the  atmosphere  at  66°  this  gives  t  =  250°. 


216  STEAM-BOILEK  ECONOMY. 

Taking  c,  the  specific*  heat  of  the  gases  at  0.24,  we  have 
for    /      =      20  30 


rf    = 

4.8 

7.2 

tcf  = 

1200 

1800 

B 

K  -  tcf 

0.919 

0.878 

K 

BEP  = 

14.08 

13.46 

X 

T  —  —  = 

3083 

2056 

We  cannot  find  A  from  the  equation  A  =  -—  -—  -,  since  a  is  as  yet 


, 


unknown.     We  therefore  obtain  it  from  eq.  (11)  : 

BE 


which  gives 


. 

~ 


W 

S' 


r     BEP          ,-i  s 

=  LlT^S/F    '  E'\  W 


Making  the  computations,  we  obtain  for  the  economy  trials: 
For/=  20: 


1 

BEp 

Root. 

Firm. 
13.387 

Lowe. 
13.453 

Smith. 
13.581 

B.  &W. 
13.582 

Gal. 
13.751 

.  +  RS/W 

Ea 

=  12.094 

11.988 

11.923 

11.906 

11.822 

11.583 

Difference 

=    1.460 

1.399 

1.530 

1.675 

1.760 

2.168 

Mult 

.  by  —,A 

=      .565 

.725 

.713 

.601 

.630 

.518 

A(T  —  t) 

n,  — 

ftftfi 

49ft 

491 

3*?; 

S79 

QAA 

And  for/=  30: 
BE 


,    ,        '.,„  =  12.963        12.800        12.868  12.989  12.989        13.150 

i  -p  zto/  W 

A  =      .336            .421            .439  .389  .418  .374 

a  =     132             165             173  153  164  147 

Using  the  same  values  of  K,  f,  and  R  for  the  capacity  trials,  we 
obtain : 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


217 


For/  =  20: 
BE 


Root. 


Ea  =  10.441 
Difference  =     3.217 
8 


Mult,  by  ~,  A  = 


BEp 


1.004 
a  =   592 
And  for/=  30: 

=  13.056 


Firm. 
13.489 

11.064 
2.4-25 

1.060 
625 


Lowe. 
13.644 

11.163 

2.481 

.782 
461 


Smith. 
13.714 

11.925 
1.789 

.478 
282 


B.&W. 
13.728 

10.330 
3.398 

.883 
521 


Gal. 

13.784 

11.216 
2.568 

.544 
321 


R8/W 

A  =      .816 
a  =   321 


12.895        13.043        13.110        13.124        13.177 


.800 
314 


.572 
235 


.316 
124 


.726 

285 


.416 
163 


The  calculated  values  of  a  are  therefore,  for  the  several  cases  and 
for  the  different  assumptions,  seen  to  vary  between  the  wide  limits  of 
124  and  625.  The  higher  figures  obtained  in  the  capacity  trials  with 
f  taken  at  20  are  improbable,  since  it  is  likely  that  with  the  stronger 
draft  and  the  comparatively  low  economy  obtained  the  air-supply  was 
much  greater  than  that  corresponding  to  a  value  of/  =  20. 

The  results  of  two  tests  reported  by  J.  C.  Hoadley  in  Van  Nos- 
trantfs  Magazine  in  1882  give  the  data  required  for  computation  in 
more  complete  form,  and  leave  less  room  for  assumption. 

In  these  tests  the  following  data,  are  given,  or  may  be  calculated 
from  the  data  given : 

Bahcock  and  Return 

Wilcox  Tubular 

Boilers.  Boilers. 

Heating  value  per  Ib.  of  combustible K  =  14,344 

"  "     in  evaporation  units,  K -s-  965.7  Ep  —          15 

Water  evap.  from  and  at  212°  per  Ib.  combustible,  Ea  =  11.255  10.571 

Efficiency,  Ea  -?-  Ep percent     75.03  70.47 

Flue-gases  per  Ib.  combustible ./  =     30.71  32.10 

Mean  temperature  of  flue-gases T?  -f-  60  =        467  543 

Loss  of  efficiency  due  to  heat  in  the  flue-gases,  percent     20.54  25.47 

All  other  losses,  including  radiation,  per  cent 4.43  3.43 

Temperature  of  fire,  calculated  by  Mr.  Hoadley 1886°  F. 

"              found  by  pyrometer  in  hottest  part  of  fire    2270° 

Calculating  the  elevation  of  the  temperature  of  the  fire 
above  that  of  the  atmosphere  (60°)  by  the  formula 

Tl=jj,  gives 1946°  1862° 

CJ 

Temp,  of  steam  above  atmosphere 279°  2793 

f   _  i 

Calculated  value  of  B=  — ^ — - 8566  .8502       1 

1 1 

BEV  — 12.849  12.753 


218  STEAM-BOILER  ECONOMY. 

Water  evaporated  from  and  at  212°  per  sq.  ft.  heating 

surface W  -f-  S  =       3.99  5.27 

Taking  R  =  0.1,  we  have         B^j        = 12.534  12.525 

Subtract^ 11.255  10.571 

Gives  A-a*  = 1-279  1.954 

o 

From  which  A  = 321  .371 

a  =  A^T~  t}  = 72.6  76.3 

These  figures  and  the  ones  given  above  for  the  value  of  a  indicate 
that  it  has  a  much  wider  range  than  that  given  by  Rankine,  viz.,  160 
to  200.  The  very  low  figures  obtained  from  Hoadley's  tests  are,  how- 
ever, probably  inaccurate,  and  the  following  may  be  given  as  a  reason 
to  account  for  them. 

A  high  evaporative  result,  according  to  the  formula,  is  consistent 
with  a  low  value  of  either/ or  a.  If  a  high  result  is  obtained,  and  a 
high  value  of  /is  found  from  the  analysis  of  the  chimney-gases,  then 
the  value  of  a,  the  unknown  quantity,  which  can  be  obtained  only  by 
computation,  using  the  formula,  will  appear  to  be  low.  The  formula, 
however,  is  based  on  the  supposition  that  /  is  the  weight  of  gas 
in  the  furnace  per  pound  of  combustible;  but  the  weight  of  the  gas  in 
the  chimney  may  be,  and  often  is,  very  much  greater,  on  account  of 
leaks  of  air  through  the  brick  setting,  between  the  furnace  and  the 
chimney.  Hoadley  gives  the  CO,  in  the  chimney-gas  as  ranging 
from  7.00  to  8.00  per  cent  by  volume;  very  low  figures,  probably 
much  lower  than  that  present  in  the  gases  just  as  they  left  the  furnace. 
If  the  samples  of  gas  for  analysis  had  been  taken  from  a  point  near  the 
furnace,  instead  of  from  the  flue  leading  to  the  chimney,  higher  figures 
for  CO,  might  have  been  found,  which  would  have  made /lower  and  a 
higher. 

Calculations  of  values  of  a  obtained  from  the  results  of  other  boiler 
trials  will  be  given  in  a  later  chapter. 

General  Formulas  for  Efficiency, — If  in  eq.  (10), 

BEP  W 

-*^a  rf    ~~    •**• rr~J 

O  O 

we  substitute  the  values  of  B  and  A,  viz., 

K  -  tcf  off* 

B  =  ^— -     and     A  =   rr       ,  „. 


we  obtain 


EFFICIENCY  OF  THE  HEATING  SURFACE.  219 


Rw 

an  equation  in  which,  if  we  consider  c,  the  specific  heat  of  the  flue- 
gases,  as  a  constant,  =  0.24,  there  are  no  less  than  six  variables,  viz., 
K,  t,  fy  R,  W/S,  and  a.  For  a  given  fuel  and  a  given  steam-pressure 
in  the  boiler  K  and  t  may  also  be  taken  as  constants. 

Since  Ep  =  K  -4-  966,  we  may  write 

_          K  -  tcf  g^f       W 

966  (l  +  RyjFl 
Also  the  efficiency 

Ea  K  -  tcf 


(~\  ^i\ 

E*  "  TA,  ,  Bs\     z  (x-tcf)a' 


Interpretation  of  Equation  (13), — For  a  given  fuel,  completely 
burned  in  the  furnace,  and  a  given  steam-pressure,  the  evaporation 
per  pound  of  combustible  will  depend— 

1.  On  the  heating  value  of  the  combustible,  or  K. 

2.  On  the  elevation  of  the  temperature  of  the  water  in  the  boiler 
above  the  atmospheric  temperature,  or  t. 

3.  On/,  the  weight  of  flue-gases  per  pound  of  combustible,  which 
depends  on  the  force  of  the  draft  and  on  the  thickness  of  the  bed  of 
fuel  and  other  obstructions  to  the  draft,  such  as  choked  air  or  gas 
passages,  clinker  on  the  grates,  etc. 

4.  On  the  rate  of  driving  W /S,  which  depends  on  the  quantity  of 
fuel  burned  per  square  foot  of  heating  surface. 

5.  On  the  loss  by  radiation,   which  may  be   reduced  to  a  small 
amount  by  diminishing  the  extent  of  radiating  surface  and  by  clothing 
it  with  non-conducting  material. 

6.  On  the  value  of  the  coefficient  #,  which  is  not  merely  a  coefficient 
of  the  resistance  to  conduction  of  heat  through  the  metal  plates  of  the 
boiler,  as  it  has  hitherto  been  considered  in  theoretical  discussions  of  the 
subject,  but  is  also  a  function  of  the  method  in  which  the  gases  pass 
over  the  heating  surface,  and  of  the  proportion  of  the  whole  heating 


220  STEAM-BOILER  ECONOMY. 

surface  which  is  properly  covered  by  the  currents  of  hot  gas  as  they 
pass  from  the  furnace  to  the  chimney-flue,  not  teing  "  short-circuited  " 
or  covered  by  eddies  of  cool  gas.  If  a  boiler  has  its  heating  surface 
of  moderate  thickness,  clean  inside  and  out,  and  the  water  on  one  side 
has  a  circulation  sufficient  to  sweep  away  steam  or  air-bubbles  as  fast  as 
they  form  on  it,  the  value  of  the  coefficient  a  should  be  low;  but  if 
under  these  favorable  conditions  the  gas-passages  have  such  an  ar- 
rangement or  such  proportions  as  to  allow  of  the  short-circuiting  of 
the  current  of  gas  or  the  formation  of  eddies  of  cool  gas,  then  the 
value  of  a  may  be  high.  It  should  be  noted  that  the  coefficient  a  as 
here  used  is  not  a  "constant  of  nature"  whose  value  is  derived  from 
direct  experiments  on  heat  transmission,  but  is  only  the  result  of  com- 
putation of  a  complex  formula(  see  Eq.  16)  which  contains  six  other 
variables.  Any  error  in  the  observed  data  which  affects  the  value  of 
any  of  these  variables  will  therefore  affect  the  computed  value  of  a. 

Large  values  of/,  R,  and  W/S  indicate  losses  of  heat  due  respect- 
tively  to  excessive  supply  of  air,  to  excessive  radiation,  and  to  exces- 
sive rate  of  driving.  A  large  value  of  a  indicates  a  loss  of  heat  which 
may  be  due  to  one  or  more  of  several  causes,  such  as  excessive  thick- 
ness or  defective  conducting  power  of  the  metal,  coatings  of  scale  or 
grease  on  one  side  of  the  metal,  or  of  soot  or  dust  on  the  other,  short- 
circuiting  of  the  gases,  or  imperfect  combustion.  The  multifarious- 
ness  of  this  coefficient,  therefore,  may  cause  it  to  have  a  very  wide 
range  of  values,  say  from  100  to  500,  instead  of  the  narrow  range,  160 
to  200,  given  by  Eankiiie. 

The  Coefficient  a  as  a  Criterion  of  Boiler  Performance. — If  we  have 
the  following  data  obtained  from  the  test  of  a  boiler: 

K  =  heating  value  per  Ib.  of  combustible; 
W/S  =  evaporation  per  sq.  ft.  of  heating  surface  per  hour; 
t  =  temperature  of  the  steam; 

Ea  =  evaporation  from  and  at  212°  per  Ib.  combustible, 
we  may  form  an  approximate  estimate  of  whether  or  not  the  perform- 
ance is  high  for  the  given  rate  of  driving  by  the  following  method : 

From  formula  (14)  we  obtain 

K-  tcf 
a  =  J 


For  a  high  evaporation  with  given  values  of  K,  t,  and  W/S  it  is 
necessary  that /and  R  be  low,  say/  =  20  and  R  =  0.1.     Substitut- 


EFFICIENCY  OF  THE  HEATING  SURFACE.  221 

ing  these  values  in  the  above  equation  and  taking  c  =  0.24,  we  obtain 

23.04        W 


966(^1  +-1    -   ' 

If,  on  substituting  in  this  equation  the  observed  values  of  K,  t,  W/8f 
and  Ea ,  the  value  of  a  comes  between  200  and  400,  the  performance 
may  be  considered  high;  if  much  above  400,  it  is  from  fair  to  low. 
The  cause  of  low  performance  may  be  low  temperature  of  furnace,  due 
either  to  imperfect  combustion  or  to  excessive  air-supply;  short-circuit- 
ing of  the  gases,  rendering  the  heating  surface  ineffective;  air-leaks 
into  the  setting;  moisture  in  the  coal  or  in  the  air;  unclean  heating 
surface ;  or  excessive  radiation. 

Applying  this  formula  to  the  data  of  the  Centennial  tests,  we  will 
obtain  the  same  values  for  a  as  those  already  given  on  p.  216  for/  =  20, 
K  =  14800,  t  =  250,  ranging  from  306  for  the  Galloway  boiler  to  428 
for  the  Firmenich  in  the  six  economy  tests  showing  the  best  results. 

Applying  it  to  Hoadley's  tests,  we  have : 

B.  &  W.  boilers: 

r   14344-4.8X279  -|    .  23.04  X  o.99          _ 

|_966(l-f  0.1  X  1/3.99)  J    '     14344  -  4.8  X  279   " 

Tubular  boilers : 
F    14344-4.8  X279  23.04  X  5.27 


"1    . 

J    ' 


" 


L966(l+0.1  X  1/5.27)  J    '     14344  -  4.8  x  279 

W 
Effect  on  Ea  of  Variations  of/,  R,  -^,  and  a.—  We   shall    now 

make  some  computations  of  different  values  of  Ea ,  or  the  evaporation 
from  and  at  212°  per  pound  of  combustible,  based  on  assumed  con- 
stant values  of  K,  t,  and  c,  and  various  values  of/,  R,  a,  and  W/  S. 
Assume  that  the  coal  is  anthracite,  with  a  heating  value  of  K=  14,800 
B.T.U.  per  Ib.  combustible  ;  that  t  =  300°,  corresponding  to  steam 
of  140  Ibs.  gauge  pressure,  and  atmospheric  temperature  of  60°;  and 
c,  the  specific  heat  of  the  flue-gases,  =  0.24.  Then  tc  =  72; 

Ep  =  14,800  -4-  966  =  15.321; 

__  14,800  -  72/* 
tt~         14,800  .05760/'  W 

/\     J.  t/ •  tj /V  A.     ™""~     ^~~~i     /->/~v  r\  fvr*  !?•      ^^        rV~  • 


„   8  14,800  -  72/ 

•  +  -»  w 


222  STEAM-BOILER  ECONOMY. 

Kow  assume  that  /  =  20  and  a  =  200,  and  with  four  different 
values  of  R,  viz.,  0,  0.05,  0.1,  and  0.2,  calculate  the  effect  of  radiation 
upon  the  values  of  the  actual  evaporation  per  Ib.  combustible,  Ea,  and 
the  efficiency,  Ea  -=-  Epi  for  different  rates  of  driving,  W*  -T-  S.  The 
results  are  as  below : 

Values  ofEa  and  EJEp  with  K  -  14,800,  t  =  300,  /  =  20,  a  =  200. 
W/S=  123468 

#  =  0,      Ea          =lbs.  13.485      13.140      12.795      12.450      11.761      11.071 
EJE     =  %     88.01        85.76        83.51        81.26        76.76        72.26 
J?  =  0.05,  Ea         =lbs.  12.827      12.803      12.568      12.280      11.647      10.985. 

EJE   =  %     83.72        83.56        82.03        80.15        76.02        71.70 
E  =  Q.\,  Ea         =lbs.  12.228      12.482      12.350      12.113      11.534      10.901 
EJEp  =  %     79.81        81.47        80.61  -     79.06        75.28        71.15 
fi  =  Q.2,Ea     P=  Ibs.  11.180      11.883      11.930      11.782      11.315      10.734 

EJE     —  %    72.97        77.56        77.87        76.97        73.85        70.06 
To  determine  the  effect  of  various  values  of  /,  or  the  weight  of 
dry  chimney-gases  per  pound  of  combustible,  upon  the  evaporation 
and  efficiency,  take  R  =  0.1,  a  =  200,  and  /  =  20,  25,  30,  and  35. 
The  computation  gives  the  results  below : 

Values  of  Ea  and  Ea/Ep  with  K  =  14,800,  t  =  300,  R  =  0.1, 

a  —  200,  /  =  20  to  35. 

W/S=                      123  4  68 

f=2Q,Ea        =  Ibs.  12.228        12.482        12.350  12.113  11.534  10.901 

"       Ea/Ep  =  %  .      79.81          81.47          80.61  79.06  75.28  71.15 

/=25,   Ea       -  Ibs.  11.681        11.710        11.363  10.916  9.915  8.863 

"      Ea/Ep  =  %        76.24          76.43          74.17  71.25  64.71  57.85 

f=W,Ea       =  Ibs.  11.076        10.823        10.203  9.486  7.950  6.362 

"      Ea/Ep  =  %        72.29          70.64          66.59  61.92  51.89  41.52 

f=35,Ea       =  Ibs.  10.407          9.808          8.853  7.805  5.608  3.361 

"       Ea/Ep  =  '%        67.93          64.02          57.78  50.54  36.60  21.94 

In  like  manner,  we  obtain  the  effect  of  variations  in  the  value  of 
the  coefficient  a  as  follows: 

Values  of  Ea  and  Ea/Ep  with  K  =  14,800,  t  =  300,  R  =0.1, 

/  =  20,  a  —  100  to  400. 

W/8=  123468 

«  =  100,   Ea       =  Ibs.  12.401        12.827        12.867        12.805        12.568  12.279 

Ea/Ep  -%        80.94          83.72          83.98        .83.58          82.03  80.14 

a  =  200,   Ea       =  Ibs.  12.228        12.482        12.350        12.113        11.534  10.901 

Ea/Ep  =  %        79.81          81.47          80.61          79.06          75.28  71.15 

a  =  300,  Ea       =  Ibs.  12.056        12.137        11.832        11.425        10.499  9.520 

Ea/Ep  =  %        78.69          79.22          77.23          74.57          68.53  62.14 

a  =  400,    Ea      =  Ibs.  11.883        11.792        11.316        10.734          9.464  8.141 

*        Ea/Ep  =  %       77.56         76.97         73.86         70.06         61.77  53.14 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


223 


X 


rmen'ch 


Bibcock  &\ 


Vik  ox 


5  7J  ifh 


0  illoway. 


Xb 


1  E  "5  4  5  6  7  8 

Lb$.  Water  Evaporated  from  and  at  212°  F.  per  sq.ft.  of  Heating  Surface  per  Hour. 

FIG.    49.— CURVES    OF    CALCULATED    EFFICIENCIES    FOR    DIFFERENT    RATES 

OF  DRIVING,  for  K=  14,800,  R  -  0.1,  t  —  300  (except  one  curve,  t  =  250) 

/=  20  to  35,  a  =  100  to  400. 


UJ 


70 


I  234-587 

FIG.  50.— EFFECT  OF  RADIATION  UPON  EFFICIENCY. 


224 


STEAM-BOILER  ECONOMY. 


The   Effect  of  Variation  in  the  Steam-pressure,  giving  different 
values  of  £,  the  elevation  of  the  temperature  of  the  steam  above  that 
of  the  atmosphere,  is  shown  below : 
Values  of  Ea  and  Ea/EP  withK—  14,800,  /=  20,  R  —  0.1,  a  =  200,  and  t  =  150°, 

250°,  and  300°,  corresponding  respectively  to  steam-gauge  pressures  of  0,  65,  and 

142  Ibs.,  and  atmospheric  temperature  o/62°  F. 


f;=s 

1 

2 

3 

4 

6 

8 

Hia           =- 

Ibs. 

12.924 

13.227 

13.124 

12.911 

12.375 

11.778 

iLa/  tiif  —  - 

* 

84.35 

86.33 

85.66 

84.27 

80.76 

76.87 

Jbu  .     '  j  — 

Ibs. 

12.460 

12.721 

12.613 

12.380 

11.814 

11.195 

Ea/Ep  '=• 

% 

81.33 

83.03 

82.32 

80.80 

77.11 

73.07 

En            — 

Ibs. 

12.228 

12.482 

12.350 

12.113 

11.534 

10.901 

Ea/Ep  = 

* 

79.81 

81.47 

80.61 

79.06 

75.28 

71.15 

I  234567 

FIG.  51. — EFFECT  OF  STEAM-PRESSURE  UPON  EFFICIENCY. 
Effect  of  Heating  Value  of  Fuel  on  Efficiency. — The  value  of  K,  or 
B.T.U.  per  Ib.  combustible,  may  vary  from  about  20,000  for  petroleum 
to  about  6000  for  wood.  The  formula  (13)  will  not  apply  without 
modification  to  either  of  these  fuels,  since  another  term  would  have  to 
be  subtracted,  representing  the  heat  lost  in  the  superheated  steam  in  the 
chimney-gases,  derived  from  the  combustion  of  the  hydrogen  in  both 
fuels  and  from  the  moisture  in  the  wood.  Neglecting  this  subtractive 
term  and  taking  two  hydrogenous  coals,  one  with  a  heating  value  of 
16,000  B.T.U.  per  Ib.  combustible,  about  the  highest  figure  for  semi- 
bituminous  coal,  and  the  other  with  13,600  B.T.U.,  corresponding  to 
a  highly  volatile  Illinois  coal,  assuming  f=  20,  a  =  200,  c  =  0.24, 
t  —  300,  and  substituting  these  values  in  equation  (13),  we  obtain  the 
following : 

Values  of  Ea  and  Ea/Ep  corresponding  to  K—  13,600, 14,800,  and  16,000,  no  allow 
ance  being  made  for  heat  lost  in  superheated  steam  in  the  chimney -gases. 


W/S  = 
=  13,600,  Ea 


=lbs. 


JT=  14,800,^        =lbs. 

Ea/Ep  "=  % 

JT=  16,000,  Ea        =lbs. 

Ea/EP  =  % 


1 

2 

3 

4 

6 

8 

11.065 

11.231 

11.045 

10.765 

10.108 

9.402 

78.59 

79.77 

78.45 

76.46 

71.80 

66.78 

12.228 

12.482 

12.350 

12113 

11.534 

10.901 

79.81 

81.47 

80.61 

79.06 

75.28 

71.15 

13.386 

13.722 

13.638 

13.439 

12.926 

12.353 

80.82 

82.85 

82.34 

81.14 

78.04 

74.58 

EFFICIENCY  OF  THE  HEATING  SURFACE. 


225 


This  table  shows  that,  other  conditions  being  equal,  the  highest  effi- 
ciency may  be  obtained  from  the  fuels  of  the  highest  heating  value;  also 
that  the  decrease  of  efficiency  due  to  rapid  rates  of  driving  is  greatest 


Vv/s  =       I  E  3  4  5  6  7 

FIG.  52.— EFFECT  OF  HEATING  VALUE  OF  COAL  UPON  EFFICIENCY. 

with  fuels  of  the  lowest  heating  value.  Since  for  hydrogenous  fuels 
and  fuels  containing  moisture  some  deduction,  amounting  usually  to 
upwards  of  3$,  must  be  made  from  the  possible  efficiency  calculated  by 
the  formula,  on  account  of  loss  due  to  superheated  steam  in  the  chim- 
ney-gases, it  is  probable  that  the  highest  efficiency  will  be  obtained 
from  anthracite,  although  the  semi-bituminous  coals  have  a  higher 
heating  value  than  anthracite. 

This  will  be  shown  by  the  following  example : 

Eequired  the  efficiency  obtainable  with  Pocahontas  semi-bitumi- 
nous coal  whose  analysis  is  C,  84.22;  H,  4.26;  0,  3.48;  N,  0.84;  S, 
0.59;  ash,  5.85;  moisture,  0.76,  the  dry  chimney-gas  being  20  Ibs. 
per  Ib.  of  combustible  =  /;  a  =  200,  R  =  0.1,  t  =  300.  The  theo- 
retical elevation  of  the  temperature  of  the  fire,  Tl  —  3110°,  as  cal- 
culated on  p.  30.  The  heating  value,  K,  calculated  from  the  analysis 
is  15,850  B.T.TJ.  per  pound  of  combustible. 

Ep=  15,850  -v-  966  =  16.408  Ibs.          T^-  t  =  3110°-  300°=  2810°. 
We  have  the  formula  (12),  p.  211,  for  efficiency, 


AW 


En 


in  which 


A  = 


acf        200  X  0.24  X  20 


T,  -t 
We  have  then  for 


2810 


=  0.3416. 


2-2Q  STEAM-BOILER  ECONOMY. 

~= ..   ..12  3468 

Ea  -*-  Ep  =  per  cent 80.06        81.89        81.20        79.81        76.37        72.58 

The  efficiency  calculated  by  formula  (13)  for  .7T— 16,000  is,  as  above. 

Percent 80.82        82.85        82.34        81.14        78.04        74.58 

Difference , 0.76          0.96          1.14          1.33          1.67          2.00 

The  efficiency  calculated  for  K=  14,800,  anthracite,  is 

Percent '.  79.81        81.47        80.61        79.06        75.28        71.15 

Difference -0.25       -0.42       -0.59       -0.75       -1.09       -1.43 

Showing  that  but  little  higher  efficiency  can  theoretically  be  obtained 
from  semi-bituminous  coal  of  a  heating  value  of  15,850  B.T.TJ.  per  Ib. 
of  combustible,  even  assuming  perfect  combustion  and  neglecting  the 
loss  due  to  superheated  steam,  than  from  dry  anthracite  of  a  heating 
value  of  14,800  B.T.TJ.  With  bituminous  coals  higher  in  hydrogen, 
oxygen,  and  moisture  than  the  semi-bituminous  still  lower  efficiencies 
are  obtainable. 

Let  us  calculate  the  loss  of  efficiency  due  to  superheated  steam  in 
the  chimney-gases. 

The  coal  contains  4.26$  H  and  the  combustible  4.59$.  This, 
would  make  9  X  4.59  =  41.31  Ibs.  of  H20  for  each  100  Ibs.  of  com- 
bustible. The  water  in  the  coal,  0.76$,  or  0.82$  of  the  combustible, 
adds  0.82  Ibs.  H20  to  the  gases,  making  a  total  of  42.13  Ibs.  of  super- 
heated steam,  or  0.4213  Ibs.  for  each  pouijd  of  combustible. 

Each  pound  of  this  steam  carries  away  its  latent  heat  of  evapora- 
tion at  212°,  or  966  B.T.TJ.;  the  heat  required  to  superheat  it  from 
212°  to  the  temperature  of  the  escaping  chimney-gases;  and  the 
heat  required  to  raise  1  Ib.  of  water  from  the  atmospheric  tempera- 
ture to  212°,  or  say  150°.  The  temperature  of  the  escaping  gases,  T2 , 

77*  '  T*        tj1 

may  be  calculated  as  follows  :    Formula  (1),  ~-  =  — '        2,   gives 


(~fp  '    \ 
1  — =£-  1  T7,.     But  .#/  is  the  evaporation  including  loss  by 

radiation,  or    Ea  +  r  =  ^a  ^1  -f  R  —  j,   whence 


This  gives  for  W/S  =  1,  T2  =  370°,  and  for  W/S  =  8,  T,  •=  824 
The  loss  of  heat  due  to  the  superheated  steam  then  is : 


EFFICIENCY  OF  TEE  HEATING  SURFACE.  227 

for  W/S  =  1,     0.4213  (150  +  966  +  0.48  X  370)  =  545  B.T.U. ; 
for  W/S  =  8,     0.4213  (150  +  966  +  0.48  x  824)  =  637  B.T.U. 

The  first  result  is  3.44$,  and  the  second  4.02$  of  the  heating 
value,  15,850  B.T.U.  per  pound  combustible,  reducing  the  effi- 
ciency calculated  by  the  formula  from  80.06  to  76.62,  for  W/S  =  1, 
and  from  72.58  to  68.56  for  W/S=$.  The  efficiencies  thus  re- 
duced are  respectively  3.19$  and  2.59$  below  the  corresponding  effi- 
ciencies for  anthracite. 

The  values  of  efficiency  given  in  the  tables  on  pages  222  and  224 
are  plotted  on  the  diagrams  accompanying  them.  In  Fig.  49  there  are 
also  plotted  the  values  of  the  highest  results  obtained  at  different  rates 
of  evaporation  in  the  Centennial  tests,  and,  for  comparison,  some  of 
the  lowest  results  at  different  rates  of  evaporation  in  the  same  tests. 

A  study  of  the  diagrams  leads  to  several  important  conclusions: 

1.  The  results  of  seven  Centennial  tests,  F,  L,  R,  B,  S,  and  GG, 
which  are  the  highest  reliable  results  ever  obtained  with  anthracite 
coal  for  the  rates  of  evaporation  shown,  lie  a  little  below  the  curve  of 
JT2  =  0.1,/=20,  a  =  200. 

2.  The  curve  of  R  =  0.1,  /  =  20,  and  a  =  100  lies  so  much  above 
the  curve  of  these  Centennial  tests  as  to  make  the  value  a  —  100  highly 
improbable,  although  the  two  tests  by  Hoadley  above  referred  to  give 
0  =  72.6  and  76.3  for/ =30.71  and  32.10.     There  is  no  apparent 
reason  why  a  should  be  low  when  f  is  high,  and  a  possible  explanation 
of   the  very  low  values  of  a   calculated  from  Hoadley's  results  has 
already  been  given. 

3.  The  effect   of   radiation  on  the  evaporation   is  comparatively 
small  for  values  of  R  between  0.05  and  0.2  (which  is  probably  as  high 
a  range  as  is  found  in  practice  when  the  boilers  are  well   covered) 
when  the  rate  of  evaporation  is  over  3  Ibs.  per  square  foot  of  heating 
surface  per  hour,  but  it  increases  rapidly  at  low  rates  of  evaporation. 

4.  The  effect  of  variations  of  a  within  the  limits  of  a  =  100  and 
a  —  300   increases  rapidly  with  the  increase  of  rate  of  evaporation ;, 
but  the  effect  of  increase  of  a  is  not  nearly  so  important  as  the  effect 
of  increase  of/. 

5.  The  effect  of  increase  of  /,  which  is  a  measure  of  the  air-supply  per 
pound  of  combustible,  is  of  extreme  importance,  especially  at  high 
rates  of  driving.     With  72  =  0.1  and  a  —  200  the  effect  on  Ea  of  in- 
crease of  /  with  different  values  of  W/S  is  'shown  in  the  following 
figures : 


228  8TEAM-DOILEU  ECONOMY. 

/=20  /=30  /=35 

W/S=2,  Ea  — 12.48  10.83  9.81 

"    =  4,   "   = 12.11  9.49  7.81 

"    =6,   "   = 11.53  7.95  5.61 

A  value  of/  —  20,  corresponding  to  19  Ibs.  of  air  supplied  per  pound 
of  combustible,  is  about  as  low  as  can  be  obtained  in  practice  without 
incomplete  combustion  of  a  part  of  the  fuel,  resulting  in  some  00  in 
the  furnace-gases.  The  rapid  decrease  in  economy  as  the  air-supply 
is  increased  shows  how  important  it  is  to  so  regulate  the  thickness  of 
the  bed  of  coal,  as  related  to  the  force  of  draft,  as  to  keep  the  supply 
of  air  at  or  near  19  Ibs.  per  Ib.  of  combustible. 

Value  of  c. — In  all  the  above  calculations  we  have  taken  <?,  the 
specific  heat  of  the  flue-gases,  as  constant,  =  0.24.  The  actual  specific 
heat  of  a  mixed  gas  is  found  by  multiplying  the  percentage  by  weight 
of  each  constituent  by  its  specific  heat,  adding  the  products  and  divid- 
ing by  100.  The  specific  heats  of  the  constituents  of  flue-gases  are: 
O,  0.2175;  N,  0.2438;  CO,  0.2479;  C02 ,  0.-217.  The  calculated 
specific  heat  of  flue-gases  usually  ranges  between  0.235  and  0.24.  If 
0.235  were  used  instead  of  0.24  in  computations  of  eq.  (13),  the  re- 
sults would  be  higher  by  about  half  of  one  per  cent.  It  is  probable, 
however,  that  the  figures  for  the  specific  heat  of  the  constituent  gases 
given  above,  which  are  those  given  in  most  text-books  as  the  specific 
heats  of  gases  at  ordinary  atmospheric  temperatures,  are  somewhat 
too  low  for  hot  gases.  The  figure  0.24  is  therefore  as  accurate  a  one 
as  can  be  had  with  our  present  knowledge,  but  the  average  figure,  0.237, 
calculated  from  ordinary. compositions  of  furnace-gas  is  frequently  used. 
Practical  Conclusions  derived  from  the  above  Theoretical  Dis- 
cussion.— Many  important  deductions  may  be  made  from  a  study  of 
the  figures  derived  from  equation  (13)  and  of  the  diagrams  plotted 
therefrom.  It  may  be  well  first  to  restate  the  notation  of  that 
formula: 

Ea  =  Ibs.  water  actually  evaporated  from  and  at  212°  (or  U.E.) 

per  Ib.  of  combustible; 

Ep  =  theoretically  possible  evaporation  in  U.E.  per  Ib.  of  com- 
bustible, =  K  -^  965.7; 
"Ea/Ep  =  efficiency,  usually  expressed  as  a  percentage; 

K  =  heating  value  of  the  fuel,  in  B.T.II.  per  Ib.  combustible; 
t  =  temperature  of  the  water  in  the  boiler,  minus  the  tempera- 
ture of  the  air-supply; 

c  —  specific  heat  of  the  gases,  taken  as  a  constant  =  0.24; 
/  =.  Ibs.  of  gas  per  Ib.  of  combustible; 


EFFICIENCY  OF  TEE  HEATING  SURFACE. 

R  =  radiation,  in  U.E.  per  sq.  ft.  of  heating  surface  per  hour; 
W/S  =  rate  of  driving,  U.E.  per  hour  per  sq.  ft.  of  heating  surface; 
a  =  an  experimental  coefficient  expressing  the  resistance  of  the 
plates   and   tubes  of   the  boiler  to  the  transmission  of 
heat,    together  with  certain  losses  of   efficiency  due  to 
short-circuiting  of  the  gases,  to  eddies  of  cool  gas,  etc. 
The  formula  is 

K  -  tcf 

*'  a**      W 


The  first  deduction  from  the  study  already  made  is  that  the  effi- 
ciency of  a  boiler  is  an  exceedingly  variable  quantity,  depending  on 
no  less  than  six  variable  factors,  K,  t,  f,  R,  W/S,  and  a.  Only  one 
of  these  factors,  viz.  a,  is  related  to  the  construction  of  the  boiler  and 
to  the  condition  of  its  heating  surface,  and  this  only  partly,  for  to 
some  extent  it  depends  on  the  rate  of  driving,  since  short-circuiting  of 
the  currents  of  hot  gas  may  be  influenced  by  the  rate  of  driving.  The 
value  of  R  depends  upon  the  effectiveness  of  the  protection  of  the 
boiler  and  furnace  from  loss  by  radiation.  All  of  the  other  factors  are 
functions  of  the  conditions  under  which  the  boiler  is  operated. 

The  importance  of  the  factor  a  upon  the  efficiency,  as  shown  in 
the  diagram  Fig.  49,  leads  to  the  conclusion  that,  so  far  as  possible,  the 
metal  of  the  heating  surfaces  should  be  thin;  they  should  be  kept 
clean  inside  and  out;  the  gas-passages  should  be  so  constructed  that 
the  currents  of  hot  gas  will  pass  uniformly  over  the  whole  extent  of 
heating  surface,  avoiding  short-circuiting  and  eddies,  or  the  passage 
at  greater  speed  over  some  portions  than  over  others;  the  circulation 
of  water  should  be  sufficient  to  wipe  off  bubbles  of  air  or  steam  as  fast 
as  formed;  and  the  combustion  should  be  complete. 

The  effect  of  K  on  the  efficiency,  as  shown  in  Fig.  52,  indicates 
that  the  heating  value  of  a  fuel  is  not  exactly  a  measure  of  its  practical 
value.  For  a  rate  of  driving  W/S  =  3  we  have  found,  with  /  =  20 
andrt  =  200: 

ForK=  .........................................  13.600  14,800  16,000 

Ea/Ep  =  per  cent  ................................  78.45  80.61  82.34 

KX  Ea/Ep  =  ...................  ,  ................  10,669  11,930  13,174 

While  the  heating  values  are  in  the  ratio  ............  91.9  100  108.1 

The  practical  values  are  in  the  ratio  ................  89.5  100  110.4 

If  coal  of  14,800  B.T.TJ.  per  lb.  is  worth  $1  per  ton,  coal  of  13,600 
B.T.U.  is  worth,  not  91.9  cents,  but  89.5  cents,  if  the  rateot  driving 


230  S1EAM-BOILER  ECONOMY. 

of  the  boiler  is  3  Ibs.  per  sq.  ft.  of  heating  surface  per  hour,  and  still 
less  if  the  rate  is  greater.* 

The  effect  of  the  rate  of  driving,  W/8,  shown  in  the  diagrams, 
indicates  that  for  practically  all  values  of  the  other  variables  the 
evaporation  and  the  efficiency  are  a  maximum  when  the  rate  of  driving 
is  about  2  Ibs.  evaporation  per  sq.  ft.  of  heating  surface  per  hour;  but 
that  under  fairly  good  conditions,  as  when  /  =  20,  a  =  200,  the 
efficiency  is- but  slightly  less  at  3  Ibs.  If  3000  Ibs.  of  water  per  hour 
are  to  be  evaporated,  a  boiler  of  1000  sq.  ft.  of  heating  surface  will  be 
almost  as  economical  of  fuel  as  one  of  1500  sq.  ft.,  provided  the 
boiler  is  well  constructed,  so  that  a  may  be  200  or  less,  the  coal  is  of 
good  quality,  say  K  —  14,800,  and  the  management  of  the  fire  and 
draft  good,  so  that/  =  about  20;  but  if  these  conditions  are  unfavor- 
able, then  the  boiler  of  1500  sq.  ft.  may  be  much  more  economical 
than  one  of  1000  sq.  ft.  When  good  operating  conditions  are  obtain- 
able the  small  saving  in  fuel  by  the  larger  boiler  will  probably  be  more 
than  offset  by  its  greater  cost,  so  that  practically  boilers  pro- 
portioned for  a  rate  of  driving  of  3  Ibs.  per  sq.  ft.  of  heating  surface 
per  hour  will  give  about  the  maximum  economy  of  all  costs,  including 
interest  on  investment,  depreciation,  etc.  When  fuel  is  of  very  low 
cost,  as  near  a  coal-mine,  or  when  a  boiler  is  to  be  run  at  full 
capacity  only  a  few  hours  per  day,  as  in  electric-lighting  plants, 
boilers  proportioned  for  a  much  higher  rate  of  driving  may  be  the 
most  economical  in  total  cost. 

The  effect  of  R  on  evaporation  is  seen  to  be  very  slight  at  all  rates 
of  driving  above  2  Ibs.,  but  it  increases  rapidly  at  lower  rates.  When 
the  rate  is  below  1£  Ibs.,  and  there  are  two  boilers  in  a  plant,  it  will 
usually  pay  to  shut  down  one  of  them,  driving  the  other  at  a  3-lb.  rate, 
thereby  saving  half  of  the  loss  due  to  radiation. 

The  effect  of  high  values  of/,  or  excessive  air-supply,  is  seen  to  be 
more  important  than  that  of  any  other  of  the  variable  factors  in  the 
equation.  It  is  therefore  of  the  utmost  importance  to  so  regulate  the 
draft  and  the  firing  that  the  air-supply  shall  be  no  more  than  sufficient 
to  maintain  complete  combustion.  A  very  high  furnace  temperature 
is  the  invariable  indication  of  the  best  furnace  conditions,  and  every 
effort  should  be  made  to  secure  and  maintain  this  high  temperature. 

*  The  calculation  is  based  on  /  =  20  in  each  case.  The  coal  of  K  =  13,600 
~would  be  high  in  oxygen  and  water,  and  with  it /might  be  less  than  20  without 
•causing  CO  in  the  gases.  A  lower  value  of /would  cause  the  efficiency  to  be 
higher  than  the  figure  given  in  the  table. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  231 

The  effect  of  the  temperature  of  the  water  in  the  boiler  upon  the 
•efficiency  is  not  important  within  the  limits  of  ordinary  steam-boiler 
practice;  but  a  gain  of  about  8  per  cent  in  the  evaporation,  when  the 
rate  of  driving  is  about  3  Ibs.  per  sq.  ft.  of  heating  surface  per  hour, 
might  be  effected  if  it  were  possible  to  have  the  water  in  the  boiler  of 
a  temperature  as  low  as  212°  F.  Boiler-tests  have  sometimes  been 
made  with  the  water  evaporated  at  atmospheric  pressure.  Records  of 
efficiency  obtained  in  such  tests  are  not  a  fair  measure  of  the  efficiency 
which  would  be  obtained  at  customary  steam-pressures.  The  Centen- 
nial tests  were  made  with  steam  of  70  Ibs.  gauge  pressure,  correspond- 
ing to  t  =  about  250°.  If  they  had  been  made  with  steam  of  140  Ibs., 
the  evaporation  per  Ib.  of  combustible  would  probably  have  been 
0.25  Ib.  less  in  those  tests  which  gave  the  highest  results,  reducing 
their  record  of  about  12  Ibs.  from  and  at  212°  per  Ib.  combustible  to 
about  11.75  Ibs. 

Results  corresponding  to  f  =  20  and  a  =  200,  and  an  efficiency  of 
SO  per  cent  are  scarcely  possible.  The  highest  results  obtained  in  the 
Centennial  tests  are  shown  on  the  plotted  diagram,  and  no  higher 
results  with  anthracite  have  ever  been  obtained  in  competitive  tests 
made  by  disinterested  experts  since  1876:  all  fall  below  80$  efficiency, 
and  considerably  below  the  plotted  line  of  /=  20,  a—  200,  and  t  — 
250°.  It  is  possible  to  obtain  a  value  of  a  as  low  as  200  in  a  boiler  so 
designed  and  proportioned  as  to  avoid  all  short-circuiting  of  the  gases, 
and  it  is  also  possible  to  obtain  nearly  perfect  combustion  with /as  low 
as  20  Ibs.  per  Ib.  of  combustible,  but  it  is  difficult  to  have  both  /"and  a 
at  these  low  values  at  the  same  time.  Boilers  must  be  designed  with 
flues  or  other  gas-passages  of  ample  area  to  insure  against  choking  of 
the  draft,  and  to  allow  of  the  boiler  being  driven  beyond  its  normal 
rating,  but  large  gas-passages  are  apt  to  lead  to  more  or  less  short- 
'Circuiting,  hence  to  inefficiency  of  some  portions  of  the  heating  sur- 
face, corresponding  to  high  values  of  a.  The  line  on  the  diagram  /  = 
20,  a  =  200,  must  therefore  be  considered  as  one  which  may  some- 
times, under  the  most  favorable  conditions,  be  nearly  but  never  quite 
reached,  and  an  efficiency  of  80  per  cent  as  a  little  beyond  the  best  result 
that  maybe  reached  in  practice.  With  semi-bituminous  and  bituminous 
coal  there  is  a  necessary  loss  of  efficiency  due  to  the  hydrogen  in  the  coal, 
•and  the  consequent  loss  of  heat  in  superheated  steam  in  the  chimney- 
gases.  This  loss  is  rarely  less  than  3$.  We  may  therefore  conclude 
that  about  79$  is  the  highest  efficiency  that  can  be  reached  in  practice 
anthracite  coal  and  76$  with  bituminous  or  semi-bituminous. 


232  STEAM-BOILER  ECONOMY. 

Much  higher  figures  than  these  are  sometimes  published,  but  they 
are  due  either  to  errors  in  the  boiler-test  or  to  too  low  figures  for  the 
heating  value  of  the  coal. 

The  theoretical  values  of  efficiency  given  in  the  foregoing  tables 
and  plotted  on  the  diagrams  are  all  based  on  the  supposition  that  the 
combustion  is  perfect  and  that  the  air-supply  and  the  furnace  temper- 
ature are  constant.  It  is  impossible  to  realize  these  conditions  with 
hand-firing,  since  the  opening  of  the  fire-door  and  the  firing  of  fresh 
coal  always  chill  the  furnace.  The  fresh  coal,  if  small  in  size,  checks 
the  air-supply  to  some  extent  and  tends  to  make  the  combustion  im- 
perfect for  a  short  time  after  it  is  fired.  After  the  fresh  coal  has  been 
partly  burned  away  the  air-supply  is  apt  to  be  excessive.  All  these- 
causes  tend  to  make  the  efficiency  less  than  that  given  by  the  theoret- 
ical calculation.  With  automatic  stokers,  however,  it  is  possible  to 
obtain  greater  uniformity  of  conditions,  and  consequently  a  closer  ap- 
proximation to  the  theoretical  efficiencies. 

Low  Temperature  of  Furnace  may  cause  High  Flue  Temperature. 
—  With  high  rates  of  driving  and  excessive  supply  of  air  per  pound  of 
fuel  a  large  proportion  of  the  heating  value  of  the  fuel  is  used  in  heating 
air  which  is  carried  into  the  chimney  instead  of  in  generating  steam. 
Excessive  air-supply  causes  not  only  a  low  temperature  of  the  furnace, 
but  it  may  also  cause  a  high  temperature  of  the  chimney-gases,  as  is- 
shown  by  the  following  calculation:    Take  from  the  above  tables  the 
case  of  K  =  14,800,  c  =  0.24,  t  =  300,  a  =  200,  and  W/S  =  6,  with 
four  different  values  of  /,  viz.  , 
/    =  .....................................      20  25  30  35 

#a=lbs  ..............................  ,  ----  11.534        9.915        7.950        5608 

Efficiency,  Ea/Ep  =  per  cent  ................     75.28        64.71        51.89        36.60 

Elev.  of  temp,  of  fire,  T,  ~  K  -*-<•/=  .......     3083°        2467°        2056°        1762 

We  have  £s  TI  ~  T*,  whence  flue  temperature  T,  =  T.(l  -fM, 
UP  *  i  V       UP  ' 

but  Ear  is  what  the  evaporation  would  be  if  there  were  no  radiation. 
It  differs  from  Ea,  the  actual  evaporation,  by  the  quantity 

W'~W 


AR 

pet  o  Tr  *•**• 

I  _L  ^V0  .  "  1  _J_  li. 

W  8R 

We  have,  therefore, 

Ea'-Ep  =  .............................  0.192  0.175       0.133  0.094 

Ea'            =  .............................  11.726  10.090        8.083  5.702 

EC?  -s-  Ep  =  per  cent  .....................  76.54  65.27        52.76  37.22 

T9  =  7',(1  -  Ea'/Ej)=  ...................  7*3°  857°          971°  1105* 


EFFICIENCY  OF  THE  HEATING  SURFACE.  233 

The  calculation  assumes  that  there  are  no  air-leaks  through  the 
setting  between  the  furnace  and  chimney  which  would  lower  the 
temperature  of  the  chimney-gases  and  decrease  the  efficiency. 

At  low  rates  of  driving,  excessive  air-supply  does  not  cause  so- 
great  a  rise  in  the  flue  temperature;  thus  for  W/8  =  2,  and  other 
conditions  as  above,  we  have : 


= 20  25  30             35 

Ea'            = 12.482  11.710  10.823  9.808 

Ea  -±-Ep  =  per  cent 81.47  76.43  7064  64.02. 

T!               = 3083°  2467°  2056°  1762° 

Ed-Ep- 0.590  0.530  0.459  0.376 

Ea'             = 13.072  12.240  11.282  10.184 

Ed  -=-  Ep  =  per  cent 85.32  79.89  73.64  66.47 

Ta              = 453°  496°  542°            591° 

Relation  of  Furnace  Temperature  to  Extent  of  Heating  Surface 

W 
required  for  good  Economy. — From  the  formulae  Ea'  =  BEP  —  A—^-y 

B  =  —hf, —  ?  and  A  =  -™— ^— :?  it  is  evident  that  the  actual  evapora- 
tion per  pound  or  fuel,  for  a  given  rate  of  driving  W/S,  depends  on 
the  furnace  temperature  T.  This  temperature  depends  not  only  on 
the  quantity  of  air  supplied  per  pound  of  fuel,  but  also  on  the  thor- 
oughness of  the  combustion  effected  by  it,  as  well  as  on  the  dryness  of 
the  coal  and  air  and  on  the  amount  of  direct  radiation.  An  air-supply 
of  19  Ibs.  per  Ib.  of  carbon,  making  nearly  20  Ibs.  of  gas,  will  usually 
produce  the  maximum  temperature,  a  lesser  supply  tending  to  make  the 
combustion  imperfect,  and  a  greater  causing  excessive  dilution  of  the 
gases,  both  of  which  diminish  the  temperature.  With  the  proper 
supply  of  air,  however,  combustion  may  still  be  imperfect  and  the 
temperature  low,  on  account  of  imperfect  mixing  of  the  air  with  the 
gas  distilled  from  the  coal,  irregular  firing,  too  small  space  for  com- 
bustion in  the  furnace,  or  other  causes. 

1.  Consider  a  case  in  which  combustion  is  perfect,  with  Ep  =15, 
T,  =  3000°,  t  =  300,  a  =  200,  c  =  0.24,  /  =  20,  W/8  =  3,  and 
radiation  negligible. 

T,  -  ;_3QOO-  300 
~T\~  3000 

acf      _  200  X  0.24  X  20  _ 
~~  T.  -  t  ~  2700 


Ea'  =  BEP  -  A^-  =  0.9  X  15  -  0.356  X  3  =  12.432. 


W 

S 

2.  With  other  conditions  the  same  as  above  let  T7,  =  2000°,  being; 
reduced  by  imperfect  combustion.     Then 


234  STEAM-BOILER  ECONOMY. 

2000  -  300  960 


-          2000  ' 

Ea'  =  0.85  X  15  -  0.565  X  3  =  11.055. 

3.  Find  the  value  of  W'/S  which  with  T,  =  2000°  will  give  an 
evaporation  of  12.432. 

Ea'  =  BEp  -  jjyrj     12.432  =  0.85  X  15  -  0.565^; 

whence  W'/S  =  0.320  -  0.565  .=  0.566. 

This  means  that  in  order  to  obtain  the  same  capacity  and  the  same 
economy  combined  from  a  boiler  with  a  furnace  temperature  of  2000° 
as  can  be  obtained  with  3000°,  under  the  conditions  named,  it  would 
be  necessary  to  increase  the  heating  surface  in  the  ratio  of  3  to  0.566, 
or  over  five  times.  The  case  is  still  worse  if  radiation  is  taken  into 
account,  for  the  loss  by  radiation  per  pound  of  fuel  burned  is  much 
greater  at  very  low  than  at  moderate  rates  of  driving.  Let  r  =  loss 
by  radiation,  in  units  of  evaporation  per  pound  of  fuel,  then  Ea'  —  r 

W 
—  BEP  —  A-y-.     If  r  in  the  last  case  =  0.32,  then  Ea'  =  12.43  -f  32 

W 

=  12.75  —  0.565-^-,  whence  W'/S  =  0;    that  is,  the   evaporation 

(including  radiation)  of  12.43  U.E.  per  Ib.  fuel  could  not  be  reached 
by  any  enlargement  of  heating  surface  whatever  if  the  furnace  tem- 
perature were  as  low  as  2000°. 

4.  Suppose  the  furnace  temperature  is  reduced  not  by  imperfect 
combustion  but  by  excessive  air-supply.     Let  /  =  30  Ibs.  and  T  = 
2000°. 

acf  200  X  24  X  30 

B  =  0.85  as  before;  A  =  T    J_f  =  -         17Q()        ~  =  0.847; 

Ea  —  0.85  X  15  -  0.847  X  3  =  10.21  for  W'/S  =  3. 

5.  With/  —  30,  required  W'/S  to  make  Ep  =  12.43. 

12.43  =  0.85  X  15  -  0.847  W'/S; 
W'/8=  (12.75  —  12.43)  ~  0.847  =  0.37, 

a  figure  which  would  probably  be  reduced  to  0  by  radiation. 

Examples  3  and  5  show  that  high  furnace  temperature  is  even  a 
more  important  factor  of  economy  than  extent  of  heating  surface. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  235 

A.  Blechynden's  Experiments  on  Transmission  of  Heat  through 
plates  from  hot  gases  on  one  side,  to  water  on  the  other.*  In  these 
experiments  the  water  was  contained  in  a  cylindrical  iron  vessel  of 
tinned  iron  plate,  24  W.  G.  in  thickness,  with  the  steel  plate  to  be 
tested  soldered  in  the  bottom.  The  vessel,  protected  from  radiation 
l>y  air-spaces  and  asbestos  felt,  was  placed  above  a  fire-brick  furnace, 
the  lower  half  of  which  was  filled  with  asbestos  lumps  or  balls,  covered 
with  wire  gauze*  Jets  of  gas  were  burned  among  these  balls,  gener- 
ating a  high  temperature  in  the  products  of  combustion  in  the  upper 
part  of  the  furnace.  The  hot  gases  were  allowed  to  escape  through 
four  small  horizontal  pipes  at  the  top  of  the  furnace,  on  four  sides,  so 
that  the  plate  was  exposed  on  its  bottom  surface  to  hot  gas  at  a  prac- 
tically uniform  temperature. 

Experiments  were  made  on  five  plates  of  different  thicknesses,  viz., 
plate  A,  originally  1.1875  in.  thick,  and  reduced  in  four  successive 
operations,  by  machining,  to  0.125  in.  thick;  plate  B,  four  thick- 
nesses, from  0.4688  in.  thick  to  0.1562  in.  thick;  plate  C,  0.8125  in.; 
plate  D,  0.5  in.;  plate  E,  1.1875  in.,  and  0.1875  in.  Plates  A,  B 
and  D  had  one  side  machined,  and  the  other  side  (that  exposed  to  the 
fire)  left  with  the  natural  surface,  as  it  came  from  the  mill.  Plate  C 
had  both  sides  untouched,  and  plate  E  both  sides  machined. 

The  temperature  of  the  furnace  was  determined  by  a  Siemens 
copper-ball  pyrometer.  In  some  cases  an  iron  ball  was  used  instead. 
The  specific  heats  of  both  were  compared  with  that  of  a  piece  of  plati- 
num, and  the  temperatures  recorded  depend  upon  Pouillet's  determin- 
ation of  the  specific  heat  of  platinum,  as  in  the  following  table: 

Temp.  C. 

Between  0  and  100 
0  "  300 
0  "  500 
0  "  700 
0  "  1000 
0  "  1200 

The  following  results  were  obtained  in  the  experiments:  T—  t 
being  the  difference  between  the  temperature  F,  of  the  gas  below  the 
plate  and  the  water  above  it,  q,  the  quantity  of  heat  transmitted 
in  British  thermal  units  per  hour  per  square  foot,  and  <z,  coefficient  of 
transmission  calculated  from  the  formula 

*  Trans.    Inst.   Naval   Architects,    1894;   Also   Donkin's   "Heat  Efficiency  of 
Steam-boilers,"  p.  145. 


Temp.  F. 

Platinum, 
Sp.  Ht.  (Pouillet). 

Iron, 
Sp.  Ht. 

Copper, 
Sp.  Ht. 

32  and  212 

0.0335 

0.1095 

0.0961 

32  "   572 

.0343 

.1189 

.0997 

32  "   932 

.0352 

.1279 

.1032 

32  "  1292 

.0360 

.1374 

.1068 

32  "  1832 

.0373 

i  .... 

melts. 

32  "  2192 

.0382 

236  STEAM-BOILER  ECONOMY. 

(T-t)*  (T-t\* 

q  —  v >         or      a  —  ?L_ 

a  q 

PLATE  A,  1.1875  IN.  THICK. 

T-t= 848  993          1,013          1,213          1,228          1,27S 

q  = 10,800        14,760        15,480        22,740        24,480        26,760 

o= 66.6  66.8  66.3  64.7  61.6  61.0 

PLATE  A,  0.75  IN.  THICK. 

T-t- 626     788     913    1,058    1,233 

q  = 6,840   10,920   14,640   20,280   27,120 

a= 57.2     56.9     56.9     55.2     56.1 

PLATE  A,  0.562  IN.  THICK. 

T-t= 563  708  963          1,148 

0= 6,720        10,200        19,440        29,520 

a= 47.2  49.1  47.7  44.6 

PLATE  A,  0.25  IN.  THICK. 

T-t= 503     646     723     828     893     97£ 

q= 5,940    9,240   11,880   15,420   18,480   22.620 

a= 42.6     45.2     44.0     44.5     44.2     42.3 

PLATE  A,  0.125  IN.  THICK. 

T-t-      738          908  993        1,083        1,123        1,133        1,138        1,318 

q  =  12,180      18,840      24,000      27,600       30,600       30,900      31,320      45,120 
a=     44.7          43.7          41.1          42.5          41.2          41.5         41.3          38.5 

PLATE  B,  0.4687  IN.  THICK. 

T-t  =413  638  643  993         1,028        1,123        1,128        1.14& 

q=  4,260         9,180         9,360       23,520       25,500       30,420      30,840      31,920 
a=    39.8          44.3          44.2          41.9          41.4          41.1         41.2         41.& 

PLATE  B,  0.375  IN.  THICK. 

T-t-     650  656  958  968        1,108        1,288         1,308 

q=  9,540       10,380       22,740       22,860       30,420       41,460       43,140 
«  =    44.3          41.4          40.9          42.3          41.0          40.0          39.7 

PLATE  B,  0.25  IN.  THICK. 

T-t=  373  513  773  823  848  855  1,108  1,128  1,268 
q=  3,595  6,560  14,700  17,220  18,310  19,020  31,380  33,150  43,800 
a=  38.7  40.1  40.7  39.3  39.3  38.4  39.1  38.4  36.7 

PLATE  B,  0.156  IN.  THICK. 

T-t=     543  738  973         1,058         1,123         1,248        1,263 

q  =  7,560       13,560       24,660       28,920       32,880       43,880       42,420' 
a=    39.0  402  384  387  38.3  38.2          37.4 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


237 


T-t=     652 

q-  7,740 
a  =    54.9 


T-t=  439 
g  =  4,260 
a=  45.2 


T-l=  301 
?  =  1,440 
a=  62.9 


-«=  322 
0  =  1,980 
a  =  52.4 


763 

10,860 

53.6 


755 

13,200 

43.2 


440 

2,760 

70.0 


559 

6,000 
52.1 


PLATE  C,  0.8125  IN.  THICK. 

773           778           778  848 

11,400   10,440   11,160  12,480 

52.4    58.0    54.2  57.6 


PLATE  D,  0.5  IN.  THICK. 

738  744  768 

13,080       13,560       13,980 

41.6          40.8          42.2 

PLATE  E,  1.1875  IN.  THICK. 

644        1,073 

5,220       16,140 

79.4          71.3 

PLATE  E,  0.1875  IN.  THICK. 

743        1,128 

10,320       24,900 

535          51.1 


847 

16,200 

44.3 


879    910 

18.720  20,400 

41.3    40.6 


AVERAGE  VALUES  OF  THE  COEFFICIENT  a. 


Plate  A, 

Thickness 

1.1875  in. 

0.75  in. 

0.5625  in. 

0.25  in.        0.125  in. 

a  = 

64.5 

56.5 

47.1 

43.8               41.9 

Plate  B, 

Thickness 

0. 

4687 

0.375 

0.25 

0.156 

a  = 

41.9 

41.4 

39.0 

38.6 

Plate  C, 

Thickness 

0. 

8125 

a  = 

55.1 

Plate  D, 

Thickness 

0.5 

a  = 

42.4 

Plate  E, 

Thickness 

1. 

1875 

0.1875 

a  = 

71.9 

52.3 

Mr.  Blechynden  says:  "  The  broad  general  fact  is  evident  that  the 
heat  transmitted  through  any  of  the  plates  per  degree  of  difference  of 
temperature  of  the  water  and  the  fire  is  proportional  to  that  difference ; 
or  in  other  words,  the  heat  transmitted  is  proportional  to  the  square  of 
the  difference  between  the  temperature  at  the  two  sides  of  the  plate,  or 


Heat  transmitted  per  sq.  ft. 


—  a  constant 


(Difference  of  temperature)2 

for  each  plate  within  the  limits  of  the  experiments." 

Mr.  Blechynden  gives  this  constant,  or  modulus,  for  each  plate.  It 
is  the  reciprocal  of  the  coefficient  fl,  which  has  been  calculated  by  the 
author  from  the  average  results,  for  the  purpose  of  comparing  it  with 
the  similar  coefficient  used  by  Rankine  and  others,  and  adopted  in  the 
preceding  discussion  on  the  efficiency  of  heating  surface. 


OF  THE 

((   UNIVERSITY 

OF 

- 


238 


STEAM-BOILER  ECONOMY. 


Mr.  Blechynden  further  says :  "  The  table  shows  that  there  is  a  gen- 
eral rise  in  the  value  of  the  moduli  [a  decrease  of  a]  with  decrease  of 
thickness,  but  there  are  considerable  irregularities  in  the  curves  join- 
ing the  various  points  for  each  plate.  This  is  perhaps  no  more  than 
might  be  expected,  because  of  the  great  difficulty  of  machining  all  the 
surfaces  to  the  same  degree  of  smoothness,  and  notwithstanding  the 
precautions  taken,  the  difficulty  of  maintaining  the  surfaces  uniform- 
ly clean.  It  was  found  that  the  very  slightest  traces  of  grease  caused 
a  very  large  fall  in  the  rate  of  transmission;  even  wiping  the  surface 
of  the  plate  with  a  piece  of  rag  or  waste  was  sufficient  to  influence  the 
result  detrimentally.  That  the  smoothness  of  the  surfaces  was  an  im- 
portant factor  will  be  readily  seen  when  the  position  of  the  points  for 
the  plate  E  are  compared  with  the  others.  The  differences  are  due  to 
A  and  B  having  the  receiving  surface  as  from  the  mill,  while  E  was 
very  smoothly  machined. 

"The  results  of  these  experiments  certainly  point  to  the  conclusion 
that  the  thinner  the  plates  forming  part  of  the  heating  surface  of  a 

boiler  the  higher  should 
be  the  boiler  efficiency, 
always  provided  that  the 
plates  are  clean,  but  it 
will  be  evident  that  if 
the  plates  be  coated  with 
a  covering  of  scale,  or 
some  bad  conductor, 
then  the  less  must  be 
the  influence  of  the 
thickness  on  the  effi- 
ciency, while  with  a  thick 
coat  of  oil  the  influence 
might  become  practi- 
cally unimportant.  The 
fact  that  the  heat  trans- 
mission is  proportional  to  the  square  of  the  difference  of  temperature 
of  the  two  sides  of  the  plate  shows  the  importance  of  high  furnace 
temperatures." 

The  average  values  of  the  coefficient  a  obtained  from  Blechyn den's 
experiments  have  been  plotted  in  the  adjoining  diagram,  Fig.  53,  It 
will  be  seen  that  each  plate  has  a  law  of  rate  of  transmission  of  its  own. 
Plates  A  and  C  have  about  the  average  values  for  the  different  thick- 


025 


050  0.75  IXK) 

Thickness  of  Plate,  Inches. 


125 


FIG.  53. — VALUES  OP  a,  FROM  BLECHYNDEN'S 
EXPERIMENTS. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  239 

nesses,  and  a  line  plotted  from  the  formula  a  =  40  +  20  t  is  near  to  all 
the  values  obtained  from  plate  A.  The  formula  a .=  40  -f-  20 £  ±  10 
covers  the  whole  range  of  the  experiments. 

The  very  low  values  of  a  deduced  from  Blechynden's  experiments, 
viz.,  38.6  to  71.9,  as  compared  with  the  values  200  to  400,  commonly 
obtained  in  steam-boiler  tests,  are  no  doubt  due  to  the  exceptionally 
favorable  conditions  under  which  his  experiments  were  made,  all  por- 
tions of  the  plate  being  clean  and  equally  exposed  to  radiation  and  to 
contact  with  the  hot  gases,  while  in  steam-boilers  only  a  small  fraction 
of  the  heating  surface  receives  radiation  from  the  incandescent  fuel  or 
from  glowing  fire-brick,  the  surface  is  apt  to  be  more  or  less  covered 
with  soot,  dust,  scale,  or  grease,  and  the  whole  heating  surface  is  not 
equally  effective,  part  of  it  being  short-circuited  and  in  contact  with 
eddies  of  comparatively  cool  gas. 

Durston's  Experiments  on  the  Transmission  of  Heat  through 
Plates.* — A.  J.  Durston  describes  some  experiments  made  to  deter- 
mine the  temperature  of  the  hot  side  of  a  plate,  exposed  to  hot  gases, 
when  the  other  side  was  covered  with  boiling  water.  The  tempera- 
ture was  determined  by  the  melting  of  fusible  solders  on  the  hot  side 
of  the  plate.  The  following  is  a  summary  of  the  results: 

1.  Temperature  of  hot  side  of  a  clean  plate  exposed  to  gases  at  about 

1500°  F about  240°  F. 

2.  Same  with  a  layer  of  grease  ^  in.  thick  over  inside  of  vessel. . .       "      330° 

3.  Temperature  at  the  centre  of  thickness  of  a  plate between  290°  and  336° 

4.  Loss  of  efficiency  of  heating  surface  of  boiler-tubes  due  to  a  thin 

coating  of  grease,  8  to  15  per  cent  ;  mean  of  several  experiments, 

11* 

5.  Temperature  of  hot  side  of  plates  where  boiling  water  in  an  open 

vessel  under  various  conditions  ;  a  flanged  dish  2  ft.  diameter, 
2t  in.  deep,  i  in.  thick  : 

Temperature         Temp.  Hot 
of  Fire.  Side  of  Plate. 

Clean  fresh  water 2200°  280° 

Mineral  oil  gradually  added  up  to  5^ 230Q0  310° 

Fresh  water  with  %\%  of  paraffine 2100°  330° 

Fresh  water  with  2\%  of  methylated  spirits. . .      2500°  300° 

A  greasy  deposit  ^  in.  thick  on  the  plate. . . .      2500°       about  550° 

Other  experiments  with  greasy  deposits 
showed  that  the  temperature  varied  greatly, 
depending  on  the  nature  and  thickness  of 
the  deposit. 

*  (Trans.  Inst.  Naval  Architects,  1893,  also  Doukin,  "Heat  Efficiency  of 
Steam-boilers,"  p.  157.) 


"24:0  STEAM-BOILER  ECONOMY. 

6.  Temperature  of  plates  when  boiling  water  in  a  closed  vessel  at  a 

higher  temperature  than  212°  ;  using  clean  water : 

Temp.  Hot  Temp,  of          »..- 

Side  of  Plate.  Water.  Difference. 

Over  Bunsen  burner 430°  363°  67° 

Do.    blast  forge,  full  blast..         430°  344.5°  85.5° 

7.  Same,  bottom  of  vessel  coated  with  grease  : 

Over  forge-fire,  grease  TaF  in. 

thick 510°  359°  151° 

Over  grease  drier,  or  earthier  550°  351°  199° 

Do.  and  spreading  the  grease 

up  the  sides  of  the  vessel. .        617°  80°  537° 

€.  Experiments  to  determine  whether  at  higher  steam-pressures  there  is  any 
marked  addition  to  the  excess  of  temperature  of  the  hot  side  of  the  plate 
over  that  of  the  water  showed  no  marked  addition. 

Effect  of  Circulation  upon  Economy. — In  the  above  discussions 
concerning  the  several  conditions  which  have  an  influence  on  the 
economy  of  a  steam-boiler,  nothing  has  been  said  of  the  effect  of  cir- 
culation of  the  water.  It  is  contended  by  some  writers  that  some 
boilers  have  a  more  active  circulation  of  water  than  others,  and  that 
the  transmission  of  heat,  and  therefore  the  efficiency  of  the  heating 
surface,  is  greater  the  more  rapid  the  circulation;  but  the  author  is  not 
aware  that  this  view  is  supported  by  the  results  of  trials  of  steam- 
boilers.  It  is  well  known  that  a  steam-radiator  used  for  heating  air 
transmits  a  vastly  greater  quantity  of  heat  when  the  air  is  blown  upon 
it  by  a  fan  than  when  the  air  surrounding  it  is  comparatively  still — 
that  is,  merely  moving  upward  at  the  velocity  of  the  ascending  column 
of  heated  air;  also  that  a  coil  used  for  heating  water  is  more  effective 
when  the  water  is  given  a  rapid  motion;  the  reason  being  that  the 
rapid  circulation  of  the  air,  or  water,  constantly  removes  from  the 
heating  surface  the  heated  body  and  replaces  it  with  a  cool  one,  and 
the  rate  of  transmission  increases  approximately  as  the  square  of  the 
difference  of  temperature  on  the  inside  and  outside  of  the  coil.  The 
case  is  entirely  different  with  steam-boilers.  There  is  in  all  modern 
forms  of  boilers  a  rapidity  of  circulation  sufficient  to  keep  all  the 
water  surrounding  the  heating  surfaces  at  nearly  the  temperature  of 
the  steam,  so  that  the  difference  of  temperature  on  the  two  sides  of  a 
square  foot  of  heating  surface,  with  uniform  furnace  conditions,  re- 
mains practically  constant. 

If  there  should  be  a  film  of  steam,  or  a  "steam-pocket,"  on  ona 
side  of  the  surface,  keeping  the  water  from  wetting  it,  the  transmis- 
sion of  heat  would  be  greatly  diminished,  so  that  there  might  even  be 


EFFICIENCY  OF  THE  HEATING  SURFACE.  241 

-danger  of  the  plate  becoming  overheated;  but  this  condition  is  un- 
likely to  happen  in  boilers  of  any  of  the  ordinary  forms. 

Upon  this  subject  Charles  Whiting  Baker  writes  as  follows  :  * 

So  far  as  the  transmission  of  heat  upon  the  boiler  is  making  steam 
is  concerned,  the  circulation  of  the  water  in  boilers  is  of  a  good  deal 
less  consequence  than  has  sometimes  been  claimed.  I  do  not  mean 
by  this  that  it  is  not  worth  while  to  make  proper  provision  for  circu- 
lation. There  are  possibly  some  boilers  worked  with  forced  draft, 
such  as  the  tube-plates  of  marine  boilers,  where  it  is  so  difficult  for 
the  steam-bubbles  to  get  away  fast  enough  that  we  have  a  mass  of 
foam  instead  of  water  in  contact  with  the  plate.  Under  such  condi- 
tions, of  course,  the  plate  is  bound  to  be  heated;  but  I  know  of  no 
evidence  that  this  is  any  other  than  a  rare  occurrence,  even  in  boilers 
which  are  pushed  most  severely.  .  .  .  Let  it  be  understood  that  I 
am  referring  to  circulation  only  as  affecting  the  transfer  of  heat  and 
the  consequent  economy  and  capacity  of  the  boiler.  Good  circulation 
is  desirable  to  prevent  unequal  heating  of  the  boiler,  and  consequent 
straining,  and  it  may  be  desirable  in  preventing  deposits  of  scale  and 
mud  in  places  where  they  are  least  desirable;  but  that  it  has  any  ap- 
preciable effect  on  economy  and  capacity  is  not  proved,  and  probably 
cannot  be. 

Dr.  Charles  E.  Emery,  in  a  discussion  on  "Tubulous  Boilers/' 
says  :  \ 

Our  original  conception  of  "convection"  or  "circulation"  is  ex- 
emplified in  all  boilers  of  ordinary  type.  Multiplication  and  various 
arrangements  of  the  tubes  make  this  circulation  more  and  more  active 
without  changing  its  nature  until,  with  the  very  small  tubes  referred 
to  by  Mr.  Thornycroft,  the  action  becomes  violent  and  somewhat  in- 
termittent, like  a  geyser. 

We  then  have  this  progression :  a  boiler  in  which  the  circulation 
is  like  that  in  a  kettle,  with  steam  and  water  rising  at  the  centre  and 
water  descending  at  the  sides,  will  operate  satisfactorily;  so,  also, 
special  and  sectional  boilers  provided  with  water  up-takes  and  down- 
takes,  from  the  heating  surface  to  a  separate  drum,  will  circulate  on 
the  same  principles  and  operate  satisfactorily.  Curiously,  this  will  be 
the  case  whether  the  up-takes  be  large  or  considerably  contracted. 
We  know  that  vertical  boilers  will  operate  well  when  there  is  a  large 
space  around  the  tubes  for  circulation;  but  the  naval  launch  boilers 
and  Mr.  Manning's  modification  of  the  same,  where  the  shell  is 
brought  in  close  to  the  tubes  till  it  acts  like  a  corset  to  prevent  free 
circulation,  also  operates  well.  So,  also,  a  locomotive  boiler,  with 
plenty  of  room  around  the  tubes,  operates  well,  and  it  also  operates 
well  when  there  is  very  little  room  around  the  tubes;  the  fact  being 
that,  with  a  large  area  of  down -take,  a  large  quantity  of  water  is 
moved  at  a  slow  velocity,  while  with  less  area  a  less  quantity  of  water 

*  Trans.  A.  S.  M.  E.,  vol.  xix.  p.  579. 

f  Journal  Am.  Soc,  of  Naval  Engineers,  vol.  ii.  No.  3. 


24:2  STEAM-BOILER  ECONOMY. 

is  moved,  but  at  a  higher  velocity,  produced  by  a  greater  head,  due  to 
the  fact  that  less  water  is  mixed  with  the  steam  during  its  upward 
movement  and  the  density  of  the  column  is  less.  The  extreme  of  this 
progression  is  a  tube  so  long  and  narrow  that,  with  solid  water  fed  into 
the  bottom,  the  greater  part  of  the  tube  will  be  a  mass  of  foam,  and 
mixed  steam  and  water  be  discharged  continuously  or  spasmodically 
at  the  upper  end.  It  is,  moreover,  found  that  the  steam  and  water  of 
which  the  foam  is  composed  can  be  separated  in  smaller  space  than  is 
required  with  less  vigorous  ebullition.  In  other  words,  contrary  to 
our  old  ideas  of  large  steam-space,  large  disengaging  surface  and  quiet 
ebullition  to  prevent  foaming,  we  can  apparently  obtain  as  good  re- 
sults in  a  boiler  composed  of  long,  narrow  tubes,  each  of  which  foams 
vigorously,  perhaps  spasmodically,  in  true  geyser  style,  though  not 
foaming  in  the  sense  ordinarily  understood  where  water  is  carried  to 
the  engine. 

In  ordinary  boilers  the  steam  passes  upward  and  bubbles  through 
the  water  at  the  disengaging  surface,  which  plan  operates  satisfactorily 
but  with  the  geyser  type  of  boilers  there  are  differences  of  opinion 
whether  or  not  it  is  best  to  discharge  the  upward  current  of  mixed 
steam  and  water  under  the  surface  of  the  water  in  the  drum  or  en- 
tirely above  it.  Mr.  Thornycroft  advocates  the  latter,  and  this  sys- 
tem is  adopted  with  modifications  in  the  Ward  and  Belleville  boilers. 

A  gentleman  discussing  Mr.  Thornycroft's  paper  claims,  however, 
that  it  is  better  to  discharge  the  water  and  steam  from  small  tubes 
below  the  water-level  in  separating-drum.  It  may  still  be  considered 
doubtful  which  system  will  carry  least  water  to  the  steam-pipe.  In 
the  end  it  will  probably  be  found  that  each  mode  of  operation  is 
adapted  to  a  particular  set  of  conditions. 

Efficiency  does  not  Depend  on  the  Type  of  Boiler. — It  will  be 
shown  in  the  chapter  on  Results  of  Trials  of  Steam-boilers  that  boil- 
ers of  a  great  variety  of  types  have  all  given  practically  identical 
economic  results,  approaching  the  maximum  possible  results  when  the 
operating  conditions  are  favorable,  but  the  following  extract  from  the 
same  discussion  of  Dr.  Emery,  quoted  above,  may  be  given  here: 

The  economy  of  a  boiler  does  not  depend  upon  its  type,  or  the 
particular  way  the  water  is  circulated,  but  upon  the  simple  principle 
that  when  there  is  proper  circulation  of  both  the  water  and  the  pro- 
ducts of  combustion,  the  economic  result  is  a  function  of  the  average 
quantity  of  combustible  burned  per  square  foot  of  heating  surface.  It 
is  important  that  there  be  proper  circulation,  not  only  of  the  water, 
but  of  the  products  of  combustion.  Many  special  boilers  have  large 
chambers  and  curious-shaped  passages,  so  arranged  that  the  products 
of  combustion  do  not  necessarily  pass  over  all  portions  of  the  heating 
surface;  the  current  takes  the  lines  of  least  resistance,  and  while  the 
surface  actually  passed  over  is  very  efficient,  the  average  efficiency  is 
low. 

It  being  settled  that  the  economy  of  the  different  types  of  boiler  is 


EFFICIENCY  OF  THE  HEATING  SURFACE.  243 

based  on  tlie  same  law,  the  efficiency  is  frequently  very  low,  which  is 
due  generally  to  the  improper  distribution  of  the  heated  gases  over 
the  heating  surfaces,  whereby  a  large  portion  of  the  gases  can  take  a 
short  circuit  to  the  stack.  This  difficulty  is  easily  overcome  in  ordi- 
nary boilers  by  reducing  the  cross-area  for  draft,  so  that  the  whole 
heating  surface  becomes  efficient,  which  can  be  done  if  the  products 
of  combustion  either  pass  through  fire- tubes  or  between  water-tubes. 
With  tubulous  boilers  it  is  more  difficult,  as  all  possibility  of  direct 
access  must  be  given  up  if  the  tubes  are  massed  closely  together  in  a 
flue.  In  the  writer's  opinion,  the  best  form  of  boiler  for  reasonable 
rates  of  combustion  is  one  with  inclined  tubes  connected  by  up-takes 
and  down-takes  to  a  chamber  or  drum  above,  as  in  many  sectional 
boilers. 


244:  STEAM-BOILER  ECONOMY. 


APPENDIX   TO   CHAPTER  IX. 

NOTE  1,  p.  208.  —  The  integration  may  be  done  as  follows: 
Let  (T  -  0  =  x,  d(T-  t)  =  dT  =  dx,  t  being  a  constant. 

dT  rT*  1  1 

-y_i=0;-^  |£       .-      |fa=         -_+_; 

1 


__ 

ra  -  t       Tl  -  t' 

After  finding  this  formula  Kankine  proceeds  as  follows  ("  Steam- 
engine,"  p.  265): 


Let  H=  expenditure  of  heat  in  raising  the  temperature  of  the  hot 
gas  above  that  of  the  water.     Then  Tl  —  t  =  H-±cw,  whence 

r,-ya        SH/CW      _        s 

T-t~~  SH/cw  +  acw  ~  ti+a<?w'/H' 


293,  Rankine  says : 

Let  E  —  theoretical  evaporative  power  and  Ev  =  available  evapo- 
)f  1  Ib.  fuel,  in  a  boiler  in  which  the  area  of  heating  sur- 


Again,  p 

"  Let  E  =  uieoreuuai  e\c 
rative  power  of  1  Ib.  fuel,  in 
face  is  S.  Then 


_ 

E   '        '8  +  ac' 

where  B  is  a  fractional  multiplier  to  allow  for  various  losses  of  heat, 
whose  value  is  to  be  found  by  experiment.  Now  cV  is  proportional  to 
F*  V*,  where  F '=  Ibs.  of  fuel  burned  in  the  furnace  in  a  given  time, 
and  Fn  is  the  volume  at  32°  of  the  air  supplied  per  Ib.  of  fuel.  Also 
H  a  F  X  a  constant.  Hence  it  may  be  expected  that  the  efficiency 
of  a  furnace  will  be  expressed  to  an  approximate  degree  of  accuracy  by 

E.  BS 


E       S+AF' 

where  A  is  a  constant  to  be  found  empirically,  and  is  probably  pro- 
portional approximately  to  the  square  of  the  quantity  of  air  per  Ib.  of 
fuel." 


03  EFFICIENCY  OF  THE  HEATING  SURFACE.  245 

This  is  Rankine's  formula  for  efficiency  as  a  function  of  the  neating 
surface,  which  is  often  quoted,  but  it  is  not  generally  known  that  his 

fi        T  —  T 
so-called  "  efficiency,"  -^-  =  ~  --  —^  is  quite  different  from  the  effi- 

j?  '       y7        rp 

ciency  as  defined  by  Hale  and  others,  viz.  ,  -=p  =  -*-=  —  i,  which  cor- 

responds to  what  is  commonly  known  as  "  the  efficiency  of  a  boiler.'* 
Suppose  in  a  given  case  T,  =  2400,  T,  =  600,  t  =  300.  Then 
ft*  '  7^  -  Y7  1  SOO 

-=£  =  '  —  -2  =  -  —  =  75  per  cent  efficiency,  while  Rankine's  for- 
x/p  ±  £4:00 

mula  would  give  1800  -4-  2100  =  85.7  per  cent.  The  coefficients  A 
and  B  are  given  by  Rankine  as  follows: 

B.     A. 

Boiler  Class  I.  The  convection  taking  place  in  the  best  manner,  either 
by  introducing  the  water  at  the  coolest  part  of  the  boiler  and  making 
it  travel  gradually  to  the  hottest,  or  by  heating  the  feed-water  in  a 
set  of  tubes  in  the  up-take  ;  the  draft  produced  by  a  chimney  ......   1         0.5 

Boiler  Class    II.    Ordinary  convection,  chimney  draft  ..................     ^     0.5 

Boiler  Class  III.    Best  convection,  forced  draft  ----  ....................  1         0.3 

Boiler  Class  IV.    Ordinary  convection,  forced  draft  ....................     £$     0.3 

No  satisfactory  reason  is  given  for  the  adoption  of  these  values. 
These  coefficients  of  Rankine  are  quite  different  from  the  A  and  B  of 
the  formula?  (8)  and  (9)  on  page  209. 

NOTE  2,  p.  208.  —  To  obtain  formula  (5)  we  have 

ET  8  T-T 

~' 


(Tt  - 
T,  =  T1 

Substituting  this  value  of  T^  in  (4), 
T,EP  -  T,Ea' 

E*        _  = 
cwa  TE-TE'        \         T>  -  t)[(T,  -  t)Ep  -  T,Ea' 


I  _  JT.Ep-TEa'  _  \ 
'  * 


Put =  p, 

- 
Then        P  =          *L*z^  .      (PTi  +  T9Tt)£:a'  =  T?EP; 


246  STEAM-BOILER  ECONOMY. 


NOTE  3,  p.  210.— Interpretation  of  formula  (7),  E^—  BEP—A^~. 

W 

—If  -—  =  0,  Ea'  =  BEP.     That  is,  the  evaporation  per  Ib.  of  fuel 

will  be  the  greatest  when  the  evaporation  per  sq.  ft.  of  heating  surface 
is  least.  (This  will  not  be  true  when  radiation  is  considered.) 

W '  W       BE 

If  A  -^-  —  BEP,  or  -^  =  ~~r>  Eaf=  0.    This  seems  to  be  a  paradox, 
o  o  A 

for  can  th,ere  be  any  rate  of  evaporation  at  which  the  economy,  or  the 
evaporation  per  Ib.  of  fuel,  will  be  0  ?  Substituting  for  W  its  value 

FEa',  we  have  Ea'=  BEp-  ^j~~;  and  for  Ea'=  0,  BEP  =  AF  *  °, 

which,  if  BEP ,  A,  and  S  are  finite  quantities,  can  only  be  true  if 
F  =  co  .  That  is,  when  W'/S  =BEP/A,  a  finite  quantity,  the  fuel  con- 
sumption is  infinite,  and  any  actual  evaporation,  as  W,  divided  by 
infinite  F  =  0. 

The  conclusion  is  that  a  rate  of  evaporation  per  sq.  ft.  of  heating 
surface  equivalent  to  W'/S  —  BEP/A  can  never  be  reached  until  the 
fuel  consumption  F  is  so  great  that  the  final  temperature  of  the  gases 
T^  equals  their  initial  temperature  I7, ,  which  can  occur  only  with  no 
transmission  of  heat  through  the  heating  surface,  or  with  an  infinite 
fuel  consumption. 

NOTE  4,  p.  211. — Development  of  equation  (11). 

W        ^\      RSEa 

"~1F~; 


W  W 

TTT  TJ  TT7  TTT 

The  last  term  equals  A  --;     therefore    Ea  =  -    —~  —  A  —  . 


CHAPTER  X. 


TYPES  OF  STEAM-BOILERS. 

Evolution  of  Different  Forms  of  Boiler. — The  first  stage  in  the 
development  of  steam-boiler  construction  beyond  the  plain  cylinder 
boiler  was  the  recognition  of  the  fact  that  it  is  defective  in  providing 
too  little  heating  surface  for  its  first  cost,  for  the  ground  space  it 


H 

H 

H    H 

9 

H    F 

ni 

1  1 

II                        t    IK: 

I     hH     h 

H    h 

H     1—  I 

FIG.  54  — DOUBLE-CYLINDER  BOILKU. 

occupies,  and  for  the  expense  of  its  setting.  Only  about  one-half  of 
its  whole  shell  surface  is  available  as  heating  surface;  the  remainder 
serves  only  to  hold  the  steam.  Increase  of  its  diameter  involves  in- 
crease of  the  thickness  of  its  shell,  and  hence  greater  cost  per  square 
foot  of  heating  surface,  as  well  as  increase  of  area  occupied.  Increase 
of  its  length  involves  equal  increase  of  ground  space  and  of  cost  of 
setting,  besides  increasing  the  difficulty  of  suspending  it  in  such  a 
manner  as  to  avoid  dangerous  strains.  Some  radical  change  of  form 
must  then  be  found.  In  the  United  States  the  first  departure  from 
the  plain  cylinder  boiler  was  made  in  two  different  directions  in  dif- 
ferent localities.  In  blast-furnaces  additional  heating  surface  was 
provided  by  hanging  one  cylindrical  shell  below  another,  joining  the 
.two  by  short  legs.  Such  a  construction  is  shown  in  Fig.  54.  The 
upper  cylinder  was  generally  made  of  larger  diameter  than  the  lower. 
On  the  Ohio  and  Mississippi  rivers,  steamboat  boilers  were  made  by 
enlarging  the  diameter  of  the  cylinder  and  by  putting  two  flues  inside 
of  it,  the  gases  passing  under  the  boiler  and  then  returning  through 
the  two  flues  to  the  chimney,  which  was  placed  at  the  front  of  the 
boiler.  This  form  is  shown  in  Fig.  55.  This  boiler  came  into  univer- 
sal use  on  the  western  rivers,  and  into  quite  general  use  in  the  cities 

247 


248 


STEAM-BOILER  ECONOMY. 


and  towns  located  along  these  rivers.  About  fifteen  years  ago  scarcely 
any  other  kind  of  boiler  was  in  use  in  the  large  iron-mills  and  in  the 
mines  in  and  around  Pittsburg,  such  is  the  force  of  local  custom  and 


FIG.  55. — TWO-FLUE  BOILER. 

prejudice.      Now,  however,  it  is  rapidly  being  displaced  on  land 

by  modern  water-tube  boilers,  although  it  still  holds  its  own  on  the 

steamboats. 

Evolution  of  the  Steam-boiler  in  France  and  England.— In  France 

the  development  from  the 

plain  cylinder  boiler  took  a 

form  similar  to  that  of  the 

double-cylinder   boiler,  but 

with    two    lower    cylinders 

hanging  from  the  upper  one, 

as  shown  in  Fig.  56.      This 

boiler    is   commonly   called  FIG.  56. — THE  "  ELEPHANT  "  BOILER. 

the  "elephant "  boiler. 

In  England  the  plain  cylinder  boiler  developed  into  the  Cornisli 

boiler,  in  which  the  cylinder  is  made  of  larger  diameter  and  a  large 

central  flue  is  built  into  it,  in  one 
end  of  whicTi  the  grate  is  placed. 
This  boiler  is  shown  in  Fig.  57.  A 
modification  of  the  Cornish  boiler 
FIG.  57.— THE  CORNISH  BOILER.  is  the  Lancashire,  containing  two 

internal  furnaces  and  flues,  shown  in  Fig.  58.     Another  modification 

is  the  Galloway  boiler,  in  which  the  two  internal  furnaces  lead  into- 


FIG.  59.— THE  GALLOWAY 
FIG.  58. — THE  LANCASHIRE  BOILER.  BOILER. 

one  large  flue,  oblong  in  cross-section,  crossed  by  a  number  of  conical- 
shaped  water-tubes,  which  circulate  the  water  from  the  spa^o  below 


TYPES  OF  STEAM-BOILERS. 


249- 


to  the  space  above  the  flue,  baffle  the  course  of  the  gases  through 
the  flue,  and  provide  increased  heating  surface,  as  is  shown  in  Fig.  59. 
The  Lancashire  boiler  is  now  often  built  with  Galloway  tubes  crossing 
each  of  its  flues,  as  shown  in 
Fig.  60.  This  cut  also  shows, 
in  cross-section,  the  common 
form  of  setting  of  Galloway 
and  Lancashire  boilers.  The 
gases  first  pass  through  the  in- 
ternal flues,  then  return  in  the 
two  external  flues  along  each 
side,  and  finally  pass  through 
the  single  flue  under  the  shell 
of  the  boiler.  Sometimes  the 
gases  are  made  to  pass  to  the 
front  under  one  side  of  the 
shell  and  then  return  to  the 
rear  under  the  other  side.  All 
of  the  boilers  above  described  FIG.  60.-LANCAsm™  BOTLETI  WITH  GAL- 
are  open,  although  to  a  smaller  LOWAY  TUBES. 

degree,  to  the  same  objection  that  has  been  raised  against  the  plain 
cylinder  boiler — that  of  providing  too  small  an  amount  of  heating  sur- 
face for  their  cost  and  for  the  ground  space  occupied.  The  objection 
applies  less  to  the  Galloway  than  to  the  other  forms. 

The  Horizontal  Return  Tubular  Boiler. — The  American  two-flue 
externally  fired  boiler  has  developed  through  the  stages  of  five  and  ten 
flues  into  the  modern  American  horizontal  multitubular  externally 
fired  fire-tube  boiler,  containing  often  100  tubes  or  more,  of  3  or  4 
inches  diameter,  shown  in  Figs.  61  and  62. 

Fig.  61  shows  the  most  recent  form  of  this  boiler  with  butt  and 
strap  riveting  on  the  longitudinal  seams,  adapted  for  high  pressures. 
Fig.  62  shows  an  earlier  form  for  moderate  pressures,  with  the 
common  style  of  setting.  The  steam-drum  shown  on  this  boiler  is 
now  generally  abandoned,  being  considered  a  useless  and  even 
dangerous  appendage. 

In  the  return  tubular  boiler  the  objection  of  insufficient  heating 
surface  in  proportion  to  space  occupied,  is  removed  to  a  greater  extent 
than  in  any  other  boiler  with  the  exception  of  some  forms  of  water- 
tube  boilers,  and  in  regard  to  cost  it  is  about  the  cheapest  of  all  boilers 
for  a  piven  extent  of  heating  surface.  It  is  probably  in  more  general  use* 


STEAM-BOILER  ECONOMY. 


in  the  United  States  than  any  other  form  of  boiler.  As  already  stated, 
it  is  practically  not  used  at  all  in  England,  where  there  is  a  strong 
prejudice  against  it  and  in  favor  of  the  internally  fired  Lancashire  and 
Galloway  boilers.  Its  extensive  introduction  into  this  country  is  no 
doubt  due  to  its  low  first  cost.  When  well  made  of  good  material, 
when  the  water  used  is  reasonably  free  from  scale-forming  substances, 


JJJMM 

i  »**:;:  i 


m 


FIG.  61. — HORIZONTAL  RETURN  TUBULAR  BOILER. 

and  when  it  is  carefully  handled  and  frequently  inspected,  it  may  give 
satisfaction  for  long  periods  of  time,  and  so  justify  the  favor  in 
which  it  is  held.  This  type  of  boiler  is,  however,  very  liable  to  explo- 
sion, and  many  lives  are  lost  by  its  use  every  year.  The  shell  of  the 
horizontal  tubular  boiler  being  directly  exposed  to  the  fire,  it  is  espe- 
cially liable  to  be  burned  or  weakened  when  there  are  deposits  of  scale 
or  grease  upon  it.  The  circular  rivet-seams,  and  the  double  thickness 
of  plates  at  the  seams  being  exposed  to  the  fire,  are  also  elements  of 
weakness. 

As  to  economy  of  fuel,  the  horizontal  tubular  boiler  is  subject  to 
the  same  rules  as  all  other  boilers.  Maximum  economy  may  be  ob- 
tained from  it  if  the  furnace  is  of  a  kind  which  will  burn  the  coal 
thoroughly,  if  the  extent  of  heating  surface  is  sufficient  for  the  amount 
of  coal  burned,  and  if  the  passages  through  the  flues  are  so  restricted 
in  area  that  the  gases  traverse  the  upper  and  lower  rows  with  approxi- 
mately the  same  velocity.  It  is  in  this  latter  condition  that  the  hori- 
zontal tubular  boiler  is  usually  defective.  There  is  a  tendency  of  the 
liot  gases  to  pass  through  the  upper  rows  of  tubes  instead  of  through 
all  the  tubes  alike.  This  is  easily  proved  by  inserting  a  stick  of  wood, 


TYPES  OF  STEAM-BOILERS. 


251 


say  1 X  2  x  10  inches,  set  edgewise,  in  the  end  of  each  tube  in  a  vertical 
row,  nearest  the  chimney,  and  leaving  it  there  for  say  half  an  hour. 
The  sticks  in  the  upper  tubes  will  usually  be  found  to  be  burned  up, 
while  those  in  the  lower  tubes  will  be  only  charred.  This  short-cir- 
cuiting of  the  gases  may  be  avoided  by  partially  restricting  the  flow 


FIG.  62.— RETURN  TUBULAR  BOILER  WITH  SETTING. 

through  the  upper  tubes,  but  it  would  require  considerable  experi- 
menting, by  placing  thermometers  in  several  of  the  tubes,  and  varying 
the  relative  obstruction  to  the  current  in  the  different  tubes  until  all  of 
the  thermometers  showed  the  same  temperature.  Actual  tests  of 
tubular  boilers  show  results  varying  all  the  way  from  about  11£  Ibs. 
of  water  from  and  at  212°  per  Ib.  of  combustible,  down  to  8  pounds,  or 
about  30  per  cent,  with  no  difference  in  the  coal,  the  rate  of  combus- 
tion or  the  character  of  the  firing  to  explain  the  variation.  It  is  prob- 
able that  in  such  cases  some  of  the  low  figures  are  due  to  short-circuit- 
ing of  the  gases,  which  might  be  avoided  by  properly  retarding  the 
flow  through  the  upper  tubes. 

The  Vertical  Tubular  Boiler.  — If  a  horizontal  tubular   boiler   is 
filled  with  tubes,  turned  up  on  end  and  set  over  a  furnace,  it  becomos 


252  STEAM-BOILER  ECONOMY. 

a  vertical  fire-tube  boiler.  It  is  more  common,  however,  to  build  this 
type  of  boiler  with  aii  internal  fire-box  from  2  to  4  ft.  in  height.  The 
annular  space,  2  or  3  in.  wide,  between  the  fire-box  and  the  shell,  is 
known  as  the  water-leg.  The  roof  of  the  fire-box,  a  flat  sheet  into 
which  the  lower  ends  of  the  tubes  are  expanded,  is  called  the  crown- 
sheet,  and  the  flat  sheet  on  top  of  the  boiler  into  which  the  upper  ends 
of  the  tubes  are  expanded,  is  called  the  upper  tube-sheet.  The  ex- 
ternal appearance  of  such  a  boiler  is.  shown  in  Fig.  63.  The  crown- 
sheet  is  just  below  the  hand-hole  plate  seen  in  the  front  of  the  shell 
some  distance  above  the  fire-door. 

This  boiler  is  the  most  commonly  used  type  of  boiler  in  the 
United  States  for  small  powers,  say  5  to  40  H.P.  It  is  also  the  most 
dangerous  form,  and  the  one  which  explodes  oftener  than  any  other. 
As  commonly  built,  the  water-level  is  carried  a  considerable  distance 
below  the  upper  ends  of  the  tubes,  which  are  therefore  apt  to  be  over- 
heated and  unduly  expanded,  bringing  severe  strains  on  both  the  up- 
per tu  be-sheet  and  the  crown-sheet.  The  crown-sheet  is  apt  to  ac- 
cumulate a  thick  layer  of  mud  and  scale,  which  is  liable  to  cause  the 
sheet  to  crack,  and  this  may  lead  to  an  explosion. 

Increased  safety  with  this  type  of  boiler  is  obtained  by  so  con- 
structing it  that  the  upper  ends  of  the  tubes  are  submerged,  and 
by  providing  facilities  for  inspection  and  for  the  removal  of  scale  from 
the  crown-sheet. 

,The  vertical  tubular  boiler  is  usually  not  economical  of  fuel,  on 
account  of  its  being  designed  with  too  small  an  amount  of  heating 
surface  for  the  amount  of  coal  burned  in  its  fire  box,  but  it  may 
be  made  as  economical  as  any  other  boiler  if  properly  designed  and  if 
driven  at  not  too  high  a  rate.  The  fire-box  is  usually  too  low  to  allow 
of  complete  combustion  of  the  gases  distilled  from  soft  coal,  even 
semi-bituminous,  and  the  fire-tubes  are  too  short  to  absorb  the  de- 
sired amount  of  heat  from  the  hot  gases.  Recent  designs  are  much 
better  in  these  respects.  Tubes  are  made  as  much  as  18  or  20  ft. 
long,  and  fire-boxes  as  high  as  8  ft.  from  the  grate-bars  to  the  crown- 
sheet  have  been  built,  with  good  results  as  to  economy  and  smokeless- 
ness  with  semi-bituminous  coal. 

The  Webber  Vertical  Boiler,  Fig.  64,  is  set  above  a  conical  fire- 
brick furnace.  The  combustion-chamber  is  of  the  corrugated  type,  to 
allow  of  expansion  and  contraction,  as  well  as  to  provide  sufficient 
strength  without  the  use  of  stay-bolts.  The  hot  gases,  after  passing 
through  the  combustion-chamber  and  the  short  tubes  of  large  diame- 


TYPES  OF  STEAM-BOILEltS. 


253 


ter  above  it,  enter  the  brick-lined  hood  at  the  top  of  the  boiler,  and 
then  pass  downwards  through  the  long  tubesf   of  smaller  diameter, 
around  the  outer  circumference  of 
the  boiler,  and  are  discharged  into 
the   annular   flue   at   the    bottom. 
The  wall  of  the  furnace  is  perfora- 
ted with  a  number  of  small  open- 
ings  through   which   air   may   be 
admitted   above  the  fire,  in  order 
to  burn  tlie  smoky  gases  distilled 


FIG.  63.— THE  VERTICAL  TUBULAR 
BOILER. 


FIG. 


64.— THE  WEBBER   VERTICAL 
BOILER. 


from  the  coal.  The  great  distance  of  the  bottom  flue  sheet  from 
the  grate-bars,  together  with  the  conical  brick  furnace,  are  calculated, 
when  the  firing  is  carefully  done,  to  secure  nearly  perfect  combustion. 
The  Manning  Boiler,  Fig.  65,  is  a  modification  of  the  vertical  tubu- 
lar boiler,  with  structural  features  peculiar  to  itself.  It  is  largely  used 
in  the  New  England  States.  An  especial  merit  clairhed  for  it  is  econ- 
omy of  ground  space.  A  boiler  which  has  given  180  boiler  horse- 
power is  set  on  a  space  8  ft.  in  diameter.  The  difference  in  expan- 


254 


STEAM-BOILER  ECONOMY. 


FIG.  65.— THE  MAXNIXG-  BOILER. 


sion  and  contraction  between  the 
tubes  and  the  outer  shell  is  taken 
up  in  the  double-flanged  head  con- 
necting the  barrel  of  the  boiler  with 
the  outside  of  the  fire-box,  and 
forming  an  expansion  joint.  By 
means  of  this  head  the  fire-box  is 
enlarged  so  as  to  give  the  desired 
proportion  of  area  of  heating  sur- 
face to  grate  surface.  The  crown 
is  of  such  height  to  form  a  large 
combustion-chamber. 

The  outer  fire-box  shell  is  carried 
well  up  above  the  head,  and  hand- 
holes  are  placed  exactly  on  a  line 
with  the  crown-sheet.  The  tubes 
are  placed  in  straight  rows,  and  at 
right  angles  to  one  another  extend 
two  cleaning-channels  of  ample 
size.  A  bent  tube  may  therefore 
be  inserted,  and  the  crown -sheet 
thoroughly  washed  and  cleaned. 
In  the  water-leg  also  are  placed  a 
number  of  hand-holes  and  a  clean- 
ing chain  by  means  of  which  any 
sediment  that  may  accumulate  may 
be  stirred  up  and  removed. 

The  Locomotive  Boiler. — The  pe- 
culiar merits  of  the  ordinary  form 
of  locomotive  boiler,  as  used  in 
locomotives,  are  its  allowing  to  be 
crowded  into  a  limited  space  a  great 
extent  of  heating  surface,  with  a 
large  fire-box,  its  being  self-con- 
tained, requiring  no  external  fur- 
nace, and  its  great  strength,  admit- 
ting of  working  pressure  of  200  Ibs. 
and  over.  To  obtain  these  advan- 
tages many  other  things  have  to  be 
sacrificed.  It  is  expensive,  difficult 


TYPES  OF  STEAM-BOILERS. 


255 


to  clean  and  to  repair,  is  not  durable,  and  must  be  driven  with  forced 
blast.  It  is  also  not  economical  when  driven  at  the  rate  required  for 
locomotive  practice,  the  gases  leaving  the  smoke-stack  at  high  tem- 
peratures, and  at  rapid  rates  of  combustion  a  considerable  amount 
of  uiiburned  coal  is  carried  out  of  the  stack  or  into  the  smoke-box. 


EH 

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C.I  U  ""* 

FIG.  66. — LOCOMOTIVE  TYPE  OF  BOILER  FOR  STATIONARY  SERVICE. 

Nevertheless,  the  locomotive  type  of  boiler  is  not  uncommon  in 
stationary  practice,  its  chief,  field  being  for  portable  and  semi-portable 
boilers.  A  common  form  of  the  type  as  used  for  stationary  service  is 
shown  in  Fig.  66. 

The  "Scotch"  Marine  Boiler. — Boilers  for  marine  purposes  are  built 
in  a  great  variety  of  types,  including  modifications  of  the  externally 
fired  horizontal  fire-tube  and  water-tube  boilers,  and  of  the  various 
forms  of  internally  fired  boilers,  such  as  the  vertical  tubular,  the  loco- 
motive, the  Lancashire,  etc. 

Take  the  Lancashire  boiler,  Fig.  58,  with  its  cylindrical  shell  and 
two  internal  furnaces,  and  substitute  for  the  two  smoke-flues  a  com- 
bustion-chamber, a  tube-sheet,  and  a  great  number  of  small  tubes,  and 
we  have  the  first  stage  of  development  of  the  Lancashire  into  a  mod- 
ern marine  boiler.  The  next  stage  is  to  increase  the  diameter  of  the 
boiler  and  shorten  its  length,  extending  the  combustion-chamber  up- 
wards and  putting  the  nest  of  tubes  above  the  furnace-flues  instead  of 
in  their  rear,  causing  the  tubes  to  return  the  gases  toward  the  front  of 
the  boiler.  This  makes  what  is  known  as  the  "  Scotch "  boiler,  so 
called  because  it  was  first  built  on  the  Clyde.  Increase  the  diameter 
to  14  or  15  ft.,  and  put  in  three  or  four  corrugated  furnaces,  and  we 
have  the  latest  form  of  the  boiler  shown  in  Fig.  67. 

This  boiler  is  often  made  "double-ended,"  that  is,  it  is  increased  in 
length  and  furnaces  are  placed  in  both  ends,  delivering  their  gases  intc 


256 


STEAM-BOILER  ECONOMY. 


a  common  combustion-chamber  in  the  middle,  from  which  the  smoke- 
tubes  extend  to  the  chimney-flues  at  each  end. 

The  Scotch  boiler  is  now  in  almost  universal  use  in  large  ocean- 
going merchant  vessels,  but  in  the  most  recent  ships  of  war  it  has 
been  displaced  by  the  water-tube  boiler. 

The  problem  of  designing  a  thoroughly  satisfactory  boiler  for 
ocean  service  is  one  of  great  difficulty,  and  at  best  it  offers  but  a  choice 


SECTION     ON     IB     B 


SBCTIOM     ON     A   A, 


FIG.  67. — THE  SCOTCH  MARINE  BOILER. 

of  evils.  In  stationary  service,  on  land,  a  boilor  to  be  satisfactory 
must  have  abundant  grate  surface,  so  that  fires  do  not  noed  to  be 
forced;  a  large  combustion-chamber,  to  help  in  the  burning  of  the 
volatile  gases,  and  plenty  of  heating  surface  to  extract  the  heat  from 
the  gases.  In  marine  service  not  one  of  these  conditions  can  be  pro- 
vided, for  space  on  board  ship  is  too  valuable.  The  problem  may  be 
stated  thus:  in  a  fire-room  of  so  many  square  feet  area  and  so  many 
feet  high  construct  boilers  which  shall  have  the  greatest  number  of 
square  feet  of  grate  surface,  and  heating  surface  sufficient  to  absorb  65 
or  70  per  cent  of  the  heating  value  of  the  coal  when  the  coal  is  burned 
at  the  rate  of  50  Ibs.  per  hour  per  square  foot  of  grate;  at  the  same 
time  the  boiler  must  be  strong,  durable,  easily  cleaned  and  repaired, 
and  must  not  weigh  too  much  nor  carry  too  much  weight  of  water. 


TYPES  OF  STEAM-BOILERS.  257 

Until  within  recent  years  the  Scotch  boiler  has  been  the  one  which 
most  nearly  filled  these  difficult  requirements.  It  cannot  fill  them  all, 
for  it  is  heavy,  both  in  metal  and  in  water  carried,  is  costly  and  diffi- 
cult to  repair. 

The  Water-tube  Boiler. — In  the  water-tube  steam-boiler  the  heat- 
ing surface  consists  chiefly  of  tubes  of  small  diameter,  the  water  being 
contained  in  the  inside  of  the  tubes  while  the  flame  and  gases  of  com- 
bustion are  on  the  outside.  The  water-tube  type  of  boiler  forms  a 
class  broadly  distinguished  from  the  flue  or  tubular  boiler,  also  called 
the  fire-tube  boiler,  in  which  the  water  is  contained  in  a  large  exter- 
nal shell  and  the  gases  pass  through  the  flues  or  tubes.  It  is  by  no 
means  a  recent  invention,  since  boilers  of  this  type  were  made  over  a 
century  ago,  many  forms  of  them  being  shown  in  standard  treatises  on 
boilers.  It  is  only  since  the  year  1870,  however,  that  they  have  come 
into  extensive  use. 

The  great  advantages  of  the  water-tube  type  over  all  other  forms  of 
boiler,  in  point  of  safety  from  destructive  explosions,  ability  to  stand 
the  highest  pressures,  perfection  of  circulation,  compactness,  economy 
of  fuel,  etc.,  were  well  understood  many  years  ago,  but  it  required  a 
long  course  of  development  and  experiment  to  discover  what  arrange- 
ment of  parts  and  what  mechanical  details  were  necessary  to  combine 
these  advantages  with  others  not  less  essential,  such  as  durability, 
and  facility  for  cleaning  a?id  repair. 

The  form  in  which  the  water-tube  boiler  is  now  commonly  made 
consists  of  a  bank  of  tubes,  usually  4  in.  in  diameter,  and  from  12  to 
18  ft.  long,  inclined  at  an  angle  of  about  15°  from  the  horizontal,  and 
surmounted  by  a  horizontal  water-  and  steam-drum,  from  30  to  48  in 
diameter,  of  about  the 'same  length  as  the  tubes.  The  tubes  are  exv 
paneled  into  boxes  or  "headers,"  at  each  end,  and  these  are  connected 
to  the  drum  overhead  by  circulating  tubes  or  other  connections.  The 
water-level  is  carried  about  the  middle  of  the  drum,  which  on  account 
of  its  comparatively  large  diameter  offers  a  large  disengaging  surface 
which  tends  to  insure  the  production  of  dry  steam.  The  furnace  be- 
ing placed  under  the  bank  of  tubes  (or  better,  when  soft  coal  is  used 
in  a  fire-brick  oven  built  in  front  of  the  boiler)  the  flame  circulates 
amongst  them,  being  properly  guided  by  suitable  passages  so  as  to  cause 
it  to  give  up  as  much  of  its  heat  as  possible  before  being  allowed  to 
escape  into  the  chimney. 

There  are  now  several  different  makes  of  these  boilers  in  the 
market,  to  all  of  which  the  above  description  will  apply.  They  differ, 


258 


STEAM-BOILEK  ECONOMY. 


however,  in  proportions  of  parts,  in  mechanical  details,  especially  of 
the  headers  and  their  connection  to  the  drum,  in  furnaces,  in  ma- 
terial, and  in  workmanship.  The  boiler  type  itself  being  good  it  still 
requires  engineering  skill  and  good  judgment  to  determine  what  size 
of  boiler,  what  kind  of  furnace,  and  what  arrangement  of  flues 
and  chimney  should  be  adopted  to  give  the  best  results,  consider- 
ing the  character  of  work  to  be  done,  and  the  kind  of  fuel  to  be 
used. 

The  great  success  of  the  water-tube  type  of  boiler  is  chiefly  shown  by 
the  fact  that  it  is  now  being  most  extensively  adopted  by  the  concerns 
which  use  the  largest  amount  of  power,  such  as  electric  light  and 
power  stations,  cable  roads,  large  sugar  refineries,  iron  and  steel 
works  and  the  like,  which  require  thousands  of  horse-power  in  one 
plant. 

Early  Forms  of  Water-tube  Boilers.— Fitch  &  Voight's  boiler, 
used  by  John  Fitch  in  his  steamboat  on  the  Delaware  Kiver  in  1787; 
Barlow's  boiler,  patented  in  France  in  1793,  and  used  by  Robert  Ful- 
ton in  his  steamboat  experiments  on 
the  Seine,  in  France,  in  1803,  and 


FIG.  68.— FITCH  &  VOIGHT,  1787. 


FIG.  69.— JOHN  STEVENS,  1803. 


John  Stevens's  boiler,  used  in  his  experimental  twin-screw  steam- 
boat on  the  Hudson  River  in  1804,  are  three  early  forms.  They  are  all 
described  in  Thurston's  "Growth  of  the  Steam  Engine."  Fitch's 
boiler  was  a  "pipe-boiler,"  consisting  of  a  small  water-pipe  winding 
backward  and  forward  in  the  furnace,  and  terminating  at  one  end  at 
the  point  at  which  the  feed-water  was  introduced  and  at  the  other 
uniting  with  the  steam-pipe  leading  to  the  engine.  Barlow's  had  a 
nest  of  horizontal  tubes  connected  to  water-legs  at  both  ends.  Stev- 
ens's  had  slightly  inclined  tubes,  closed  at  one  end  and  connected  to  a 
water- chamber  at  the  other. 

Some  More  Recent  Forms.— The  following  notes,  with  accompany- 


TYPES  OF  STEAM-BOILERS. 


259 


ing  illustrations,  are  ta- 
ken by  permission  from 
"Facts,"  a  pamphlet  pub- 
lished by  The  Babcock  & 
Wilcox  Co.  in  1895.  They 
show  a  few  of  a  great  num- 
ber -of  designs  of  water- 
tube  boilers  that  have  been 
made  by  varying  the  form 
units,  viz.:  1,  a  tube  closed  at 


FIG.  70.— JOLY,  1857. 
or  arrangement  of  four  elementary 
one  end;  2,  a  bent  tube;  3, 
an     aggregation    of     pipes 
and     fittings;     4,  a     group 
of    straight    tubes    connec- 
ted    with     water-chambers 
at   each    end. 


FIG.  71.— FIELD,  1866. 
BOILERS   WITH    CLOSED-EN.D   TUBES. 

Joly,  1857. — A  sectional  boiler  with  vertical  drop-tubes,  each  fed 
by  an  in-ternal  tube  extending  nearly  to  the  bottom. 

Field,  1866. — A  cylinder  boiler  with  radiating  drop-tubes  fitted  to 
the  lower  side.  Field  also  used  circulating  tubes  inside  of  the  drop- 
tube. 

Fletcher,  1869 . — A  vertical  fire-box  boiler,  with  horizontal  cone- 


FIG.  72.— FLETCHEK, 


FIG.  73.— MILLER,  1870. 


260 


STEAM-BOILER  ECONOMY. 


shaped  tubes  radiating  from  the  sides  of  the  fire-box   towards  the 

centre. 

J.  A.  Miller,  1870.— Cast  headers,  to  which  were  fixed  closed-en 
tubes,  inclined  about  15°  from  the  horizontal,  with  inner  circulating 

tubes. 

Allen,  1871.— Cast-iron  drop-tubes  slightly  inclined  from  the  ver- 
tical, screwed   into  a  horizontal  tube 
at  the  top. 


FIG.  74— ALLEN,  1871.  FIG.  75.— WIEGAND,  1872. 

Wieqand,  1872.— Groups  of  vertical  tubes,  with  inside  circulating 
tubes,  connected  to  an  overhead  steam-  and  water-reservoir.  The 
lower  ends  of  the  tubes  were  closed  by  caps. 

W.  A.  Kelly,   1876.— Similar  to  J.  A.  Miller's  design  of  1870,  with 


FIG.  76.— W.  E.  KELLY,  1876. 

some  additions,  among  them  being  superheating  tubes  for  drying  the 
steam. 


TYPES  OF  STEAM-BOILERS. 


261 


Hazelton,  1883. — A  vertical  cylinder  with  radial  tubes,  commonly 
called  the  "Porcupine"  boiler.  The  upper 
portion  of  this  boiler  is  superheating  surface. 


FTG.  77  —  HAZELTON,  1883. 


FIG.  78.— GTTRNEY,  1826. 


BOILEES    WITH    BENT    TUBES. 

Gurney,  1826. — A  pair  of  vertical  steam-  and  water-reservoirs  were 
connected  at  their  bottom  and  about  half  way  up  their  height  by 
cross-pipes,  from  which  a  series  of  bent  tubes  were  projected  into  the 
fire-box.  The  lower  row  of  tubes  served  as  a  grate.  This  boiler  was 
used  in  a  steam  road-carriage. 

Church^  1832. — A  locomotive  fire-box  with  a  vertical  extension  at 
one  end,  filled  with  bent  tubes  connecting  the  sides  of  the  fire-box 
with  the  crown-sheet,  and  with  side  openings  in  the  shape  of  fire- 
tubes  extending  through  the  shell  at 
the  top,  for  taking  off  the  gases.  This 
boiler  was  also  used  for  a  road-carriage. 


FIG.  79.— CHURCH,  1832. 


PIG,  80  —  WTLCOX,  1856. 


262 


STEAM-BOILER  ECONOMY. 


Wilcox,  1856. — Stephen  Wilcox  was  the  first  to  use  inclined  tubes- 
connecting  water-spaces,  front  and  rear,  with  an  overhead  steam-  and 
water-reservoir.  The  tubes  were  bent  with  a  slightly  reversed  curve 
extending  nearly  the  whole  length  of  the  tube.  In  1869  Mr.  Wilcox, 
with  his  partner,  George  H.  Babcock,  bought  out  the  Babcock  &  Wil- 
cox boiler,  with  straight  inclined  tubes. 

Rowan,  1865. — A  series  of  units  placed  side  by  side,  each  unit  con- 
sisting of  an  upper  and  a  lower  horizontal  drum  connected  by  a  series 
of  bent-ended  heating-tubes,  and  at  their  ends,  outside  the  setting, 
with  down-take  tubes  of  large  diameter. 


FIG.  81.— ROWAN,  1865. 

Plileger,  1871.- 
G  u  r  n  e  y  IT  tubes 
were  used  for  fire- 
bars, with  a  second 
series  added  above 
for  heating  -tubes, 
and  above  them  a 
large  steam-and 
water-drum. 

Rogers  &  Bl  ac  k, 
1876. — A  series  of  U 
tubes  on  the  outside 
of  a  vertical  shell,  sur- 
rounded with  a  brick 
setting. 


FTG.  82.— PHLEGETC,  1871. 


FIG.  83.— RO 
BLACK,  18 


FIG.  84— DANCE,  1833. 


TYPES  OF  STEAM-BOILERS. 


263 


BOILERS    BUILT    OF    PIPES   AND     FITTINGS. 

Dance,  1833. — The  lower  tubes  were  used  as  grates.  Up-flow  and 
down-flow  pipes,  connected  by  special  fittings.  Steam  and  water 
capacity  very  small,  and  no  provision  for  internal  cleaning. 

Belleville,  1865. — Bent  U  tubes  screwed  into  return  bends,  a  series 
of  coils  being  placed  vertically  side  by  side,  connected  at  the  top  to  a 
sepaiating-drum  and  at  the  bottom  to  a  common  feed-pipe. 


FIG.  85.— BELLEVILLE,  1865. 


86  —  BELLEVILLE, 


Belleville,  1877. — The  bent  pipe  was  discarded  and  return  bends 
used  on  both  ends  of  a  series  of  straight  tubes. 

Kilgore,  1874. — Straight  tubes  with  return   bends,  connected  to 

cast-iron  water-chambers.      This  boiler 
'  was  introduced  quite  extensively  in  Pitts- 
burg,  but  it  had  a  very  short  life. 


FIG.  88.— WARD,  1879. 


1Z— ~-~-~  -        -V  — > 

FIG.  87.— KILGORE,  1874. 


204 


STEAM-BOILER  ECONOMY. 


Ward,  1879. — A  vertical  cylinder,  surrounded  by  a  series  of  con- 
centric coils  interrupted  twice  in  their  circumference,  on  opposite 
sides,  by  vertical  manifolds.  These  manifolds  on  one  side  were  con- 
nected by  a  radial  pipe  to  the  bottom  of  the  cylinder,  and  at  the  other 
side  to  a  circular  pipe  connecting  near  the  top  of  the  cylinder. 

Roberts,  1887. — Straight  pipes  with  return  bends,  with  "down- 
take"  pipes  outside. 


FIG.  8U.— ROBERTS,  1887. 


FIG.  90.— ALMT,  1890. 


Almy,  1890. — Straight  pipes  connected  with  elbows  and  return 
bends  to  an  overhead  steam-  and  water-reservoir  and  bottom  connect- 
ing pipes. 

Herreslioff,  1890. — Straight  tubes  with  return  bends  at  each  end. 


BOILERS    WITH     STRAIGHT    TUBES     CONNECTED     TO    WATER-CHAMBERS 

AT    BOTH     ENDS. 

Firmemch,  1875. — Flat-sided  horizontal  drums  at  top  and  bot- 
tom of  a  bank  of  straight  tubes.  Two  such  units  were  placed  A- 
fashion,  with  the  grates  between  them  at  the  bottom,  and  surmounted 
with  a  steam-drum  on  top. 

Wlieeler,  1892. — Like  the  Firrneriich,  but  with  the  tubes  set  verti- 
cally, and  the  lower  water-drums  directly  over  the  grates. 

Maynard,  1870. — A  horizontal  steam-  and  water-cylinder  above  a 
bank  of  tubes  placed  at  a  slight  inclination  from  the  horizontal  ;  the 


TYPES  Ob  STEAM-BOILERS. 


265 


ends  of  the  tubes  expanded  into  round  boxes  having  stayed  heads  con- 
nected to  the  horizontal  drum. 


FIG.  91. — FIHMENICII,  1875. 

Modern  Forms   of  Water-tube  Boilers. — The   water-tube   type  of 
boiler  did  not  come  into  any  extensive  use  prior  to  1870,  probably 


FIG.  92.— WHEELER,  1892. 


FIG.  93.— MAYNAUD,  1870. 

because  inventors  of  the  earlier  forms  did  not 
appreciate  the  requirements  of  a  thoroughly 
good  boiler,  such  as  facility  for  cleaning  and 
repair,  provisions  for  proper  circulation  of 
the  water  and  of  the  gases  of  combustion, 
and  for  insuring  dry  steam— all  of  which  are 
met  in  at  least  some  of  the  modern  forms  of 
the  water-tube  boiler.  In  1867  Mr.  John 


260 


STEAM-BOILER  ECONOMY. 


B.  Root  invented  what  is  known  as  the  Root  boiler,  and  in 
1869  the  Babcock  &  Wilcox  Company  first  put  their  boiler  on  the 
market.  Both  of  these  boilers  have  been  improved  in  some  respects 
since  they  were  first  brought  out,  the  Babcock  &  Wilcox  reaching 
practically  its  present  form  as  early  as  1873,  and  the  Root  boiler  its 
present  form  about  ten  years  later. 

The  Babcock  &  Wilcox  Boiler,  since  the  original  patents  have 
expired,  has  been  extensively  copied,  with  modifications  more  or  less 


FIG.  94.— THE  BABCOCK  &  WILCOX 

important,  and  its  general  form  may  now  be  considered  a  standard 
type  of  boiler,  the  leading  features  of  which  are  a  horizontal  drum, 
usually  about  36  in.  diameter,  the  water-line  being  carried  at  the 
middle  of  the  drum,  and  a  "bank  "  of  4-in.  tubes  inclined  about  15° 
from  the  horizontal,  the  tubes  being  usually  laid  parallel  in  horizontal 
rows  across  the  boiler,  the  vertical  rows  being  staggered.  The  tubes 
are  expanded  at  each  end  into  headers,  which  take  different  forms 
in  different  modifications  of  the  general  type.  The  front  headers  are 
connected  with  the  drum  by  short  pieces  of  tube,  and  the  rear  headers 
by  tubes  4  to  6  ft.  long. 

In  the  most  recent  form  of  Babcock  &  Wilcox   boiler,  designed 
especially  for  high  pressures,  Fig.  94,  the  header  is  a  long  corrugated 


TYPES  OF  STEAM-BOILERS. 


26T 


box  of  forged  steel,  into  which  are  expanded  the  tubes  of  one  of  the 
vertical  staggered  rows.  Opposite  the  end  of  each  tube  there  is  a 
hand-hole  plate,  held  to  its  seat  by  a  bolt  and 
nut.  As  the  rear  header,  as  well  as  the  front 
header,  is  provided  with  similar  hand-hole 
plates,  the  interior  of  the  tube  may  be  in- 
spected by  the  boiler-owner  himself,  by  having 
.  some  one  hold  a  candle  at  the  hand-hole  of 
the  rear  header  while  he  looks  in  through 
the  front  header.  The  hand-holes  are  made 
of  such  a  size  that  the  tubes  may  be  with- 
drawn or  inserted  through  them  whenever 
a  tube  requires  to  be  replaced. 

In  the  National  and  Gill  boilers,  the  prin- 
cipal feature  of  difference  from  the  Babcock 
&  Wilcox  boiler  is  the.  form  of  the  headers. 
In  the  National  boiler  the  header  is  of  ap- 
proximately a  triangular  shape,  to  take  three 
tubes,  while  in  the  Gill  boilers  the  headers 
are  made,  as  shown  in  Fig.  95,  to  take  four, 
five  or  six  tubes.  Each  header-box  is  con- 
nected with  the  one  above  it  by  an  expanded 
nipple. 

In  the  Caldwell  boiler,  Fig.  96,  a  depart- 
ure has  been  made  from  the  usual  plan  of 
staggering  the  vertical  rows    of  tubes,  arid 
they  are  placed  directly  one  above  the  other.  FIG.  95  — HEADERS  OF  THE 
In  order  to  deflect  the  gases  and  cause  them  WILL  BOILEK. 

to  completely  envelop  the  tubes,  specially  shaped  brick  are  laid  across 
alternate  spaces  between  the  tubes  as  shown  in  Fig.  97. 

The  Root  Boiler  (Fig.  98)  consists  of  an  arrangement  of  4-in.  tubes, 
inclined  about  20°  from  the  horizontal  and  set  in  a  staggered  position 
vertically,  surrounded  by  several  horizontal  steam-  and  water-drums 
about  15  ins.  in  diameter.  The  tubes  are  expanded  into  headers  which 
with  their  connections  form  a  vertical  channel  through  which  the- 
water  passes  from  the  point  where  the  lower  tube  enters  them  to  the 
top.  When  the  boiler  is  working,  water  fills  the  tubes,  and  also  about 
half  of  each  of  the  overhead  drums,  each  one  of  which  receives  the 
water  and  steam  from  the  vertical  piles  of  tubes  immediately  below  it. 
In  the  rear  of  the  boiler,  at  the  end  of  the  overhead  water-drums^ 
each  drum  has  a  vertical  pipe  terminating  in  a  drum  common  to  all 


268 


8TEAM-BOILEE  ECONOMY. 


beneath  it,  which  is  placed  at  right  angles  to  them;  and  through  these 
vertical  "down-take  pipes"  flows  the  water  of  circulation,  which  has 
parted  with  its  bubbles  of  steam.  In  this  cross-drum  the  down-flowing 


FIG.  96.  —  THE  CALDWELL  BOILER, 


meets  the  feed-water,  which  is  introduced  at  this  point,  and 
warms  it  up  to  a  temperature  sufficiently  high  to  prevent  any  trouble 
which  might  be  caused  by  unequal  expansion  in  the  boiler  parts  from 
receiving  feed-water  at  a  low  temperature.  From  this  feed-drum, 
the  mixture  of  feed  and  circulating  water  descends  through  the  large 
vertical  down-take  pipes  to  the  mud-drum  beneath.  After  leaving  the 
mud-drum,  the  water  passes  from  the  "goose-neck"  connections  into 
the  extreme  lower  end  of  each  one  of  the  rear  vertical  sections  of  boiler- 
tubes;  and  then  it  rises  up  along  the  tubes,  maintaining  the  constant 
upward  flow  which  is  always  going  on  when  the  boiler  is  in  operation. 
The  water,  filled  with  its  bubbles  of  steam,  rises  along  the  inclined 
tubes,  and  passes  up  along  the  front  headers  into  the  overhead  water- 
drums.  At  the  rear  end  of  each  drum  the  steam  finds  an  opening 
into  the  steam-collecting  multiple  above,  which  is  placed  at  right 
angles  to  all  the  drums,  and  from  this  multiple  it  passes  along  the  two 


TYPES  OF  STEAM-BOILERS. 


269 


connecting-pipes  into  the  large  steam  and  separating  drum   located 
above  the  water-drums  about  the  centre  of  the  boiler. 
The  details  of  the  Root  boiler  are  shown  in  Fig.  99. 
No.  1  shows  a  "package"  consisting  of  two  tubes  with  a  header 
expanded  on  each  end.     No.  2  shows  these  packages  placed  one  upon 
the  other,  forming  a  section.       Connect- 
ing-bends    are     also    shown    in    place, 
through  which  a  circulation  of  water  is 
obtained  from  the  bottom  to  the  top  of 
the    section.       A    number    of    sections 
placed  side  by  side  go  to  form  a  com- 
plete boiler.     No.  3  shows  the  method 
by  which  these  bends  are  applied.      Between  the  bend'  which  is  ready 
to  drop  in  place  and  the  header  is  seen  the  metallic   packing-ring 


FIG.  97.— CAT. DWEL^  BOILER. 


FIG.  98.— THE  ROOT  WATER  TUBE  BOILER. 

which  drops  into  the  seat  beneath  it.  This  ring  is  shown  in  detail  in 
No.  4.  A  sectional  view,  No.  6,  shows  it  in  place.  All  these  seats  are 
milled  to  exact  size  by  special  machinery,  and  the  ring,  which  is  made 
of  an  elastic  bronze-like  metal,  is  also  finished  to  an  exact  size. 


270 


STEAM-BOILER  ECONOMY. 


The  tapered  end  of  the  connecting-bend  is  shown  in  the  enlarged 
view,  No.  5.  When  this  plug  is  forced  down  into  the  tapered  seat  of 
the  ring  it  causes  the  ring  to  expand  in  every  direction  radially,  and 
so  make  a  tight  joint.  This  bend  is  drawn  down  into  the  seat  by  bolts. 
The  heads  of  these  bolts  are  ball-shaped  and  are  received  into  similarly 
shaped  sockets  cast  in  the  headers,  which  allow  the  screw-ends  free- 
dom to  move  in  every  direction. 

All  the  water-tube  boilers  above  mentioned,  as  well  as  many  other 

variations  of  this  general  type, 
are  known  as  sectional  boilers, 
since  they  ar*  built  up  of  sec- 
tions made  by  assembling  a  num- 
ber of  interchangeable  parts. 
This  sectional  feature  is  a  con- 
venience in  transportation  and 
erection,  and  it  facilitates  the 
rapid  making  of  repairs;  a  new 
section  being  easily  substituted 
for  an  old  one. 

Other  water-tube  boilers  are 
made  which  are  not  sectional. 
One  of  the  best  known  is  the 
Heine  boiler,  shown  in  Fig.  20, 
p.  165.  The  tubes  are  parallel 
with  the  drum,  both  being  in- 
clined at  the  same  angle  when 
the  boiler  is  set  up,  and  are  con- 
nected with  it  at  each  end  by 
large  water-legs,  made  of  plates 
stayed  together.  A  hand-hole 
plate  is  opposite  the  end  of  each 
FIG.  99.— DETAILS  OF  THE  ROOT  BOILER,  tube,  through  which  the  tube 

may  be  cleaned  or  replaced. 

It  will  be  noticed  that  in  the  Heine  boiler,  Fig.  20,  the  passages 
for  the  gases  of  combustion  are  horizontal,  or  parallel  with  the  tubes, 
while  in  the  other  boilers  the  gases  pass  transversely  across  the  tubes 
three  times.  For  anthracite  coal  the  transverse  passages  are  probably 
the  best,  and  when  properly  fired  this  coal  is  thoroughly  burned  on 
the  grates,  and  the  direction  of  the  gas-passages  across  the  tubes  oifers 
every  facility  that  can  be  desired  for  allowing  the  heating  surface  to 


TYPES  OF  STEAM-BOILERS. 


271 


absorb  the  heat  from  the  gases.  With  bituminous  coal,  the  settings 
shown  in  Figs.  94  and  96  do  not 
offer  sufficient  opportunity  for  the 
gases  from  the  coal  to  be  thor- 
oughly burned  before  they  reach 
the  tubes,  consequently  a  portion 
of  the  valuable  heating  gases  is  apt 
to  go  off  unburned,  since  the  tubes 
chill  them  below  the  temperature 
of  ignition.  The  long  horizontal 
passage  under  the  lower  row  of 
tubes  is  better  for  insuring  com- 
bustion of  the  gases,  but  the  re- 
turn passage  enclosing  the  tubes 
requires  to  be  carefully  propor- 
tioned as  to  its  sectional  area,  in 
relation  to  the  amount  of  coal 
burned,  so  that  the  hot  gases  do 
not  travel  along  the  upper  por- 
tion of  the  passage  only,  leaving 
the  heating  surface  of  the  lower 
portion  in  effective.  In  adopting 
either  one  of  these  styles  of  setting,  with  bituminous  coal,  there  is 
a  choice  of  evils:  in  one  style  the  gas  may  be  imperfectly  burned,  in 
the  other  the  heat  from  the  burned  gas  may  be  imperfectly  absorbed. 
With  furnaces  adapted  to  the  complete  combustion  of  the  gases  of 
bituminous  coal,  the  transverse  passages  will  usually  be  found  prefer- 
able to  the  longitudinal. 

The  Cahall  Vertical  Water-tube  Boiler,  Fig.  100,  is  another  non- 
sectional  boiler.  It  consists,  as  shown,  of  a  nest  of  nearly  ver- 
tical water-tubes  connecting  a  shallow  water-drum  at  the  bottom 
with  a  tall  annular  steam-  and  water-drum  at  the  top,  the  size 
of  which  is  sufficient  for  a  man  to  walk  around  in  it,  and  so  be 
able  to  reach  the  inside  of  the  tubes  with  a  scraper.  The  coal  is 
burned  in  a  chamber  lined  with  fire-brick,  and  the  gases,  after  being 
caused  to  traverse  the  tubes  in  a  circuitous  manner,  by  the  bafflers 
shown  in  the  cut,  escape  out  of  the  hole  in  the  centre  of  the  annular 
drum. 

The  external  furnace  of  the  Cahall  boiler  is  well  adapted  to  the 
burning  of  bituminous  coal.  There  is  no  reason  why  an  external  oven 


FIG.  500.—  THE  CATTALL  VERTICAL 
BOILER. 


STKAM-BOILER  ECONOMY. 


or  furnace  cannot  be  used  in  connection  with  boilers  of  the  Babcock 
&  Wilcox  type.  In  fact,  such  boilers  are  sometimes  set  with  such  an 
external  furnace  with  advantageous  results,  and  their  more  general 
adoption  in  future  is  probable.  With  the  highly  volatile  coal  mined 
west  of  the  Allegheny  Mountains  the  use  of  mechanical  stokers, 
together  with  external  furnaces,  is  also  likely,  with  proper  proportion- 
ing and  careful  handling,  to  improve  economy. 

The  Stirling  Boiler,  Fig.  101,  consists  of  three  horizontal  steam- 


FIG.  101. — THE  STIRLING  BOILER. 

and  water-drums  at  the  top,  and  a  single  water-drum  at  the  bottom, 
connected  by  three  sets  of  inclined  and  somewhat  curved  tubes.  A 
fire-brick  arch  is  built  above  the  grate,  and  baffle-walls  of  fire-brick 
are  placed  above  the  upper  rows  of  two  of  the  sets  of  tubes,  which 
give  a  proper  direction  to  the  heated  gases. 

The  Wickes  Boiler,  Fig.  102,  also  consists  of  an  upper  and  lower 
drum  connected  by  vertical  tubes.  By  building  a  thin  wall  of  fire- 
brick between  two  adjoining  middle  rows  of  tubes,  as  shown  in  the 
cut,  the  passage  for  gas  is  caused  to  lead  first  upwards  from  the  fur- 
nace and  then  downwards  to  the  chimney-flue.  An  external  furnace 
is  used  with  this  boiler. 


TYPES  OF  STEAM-BOILERS. 


273 


The  Climax  Boiler,  Fig.  103,  consists  of  a  central  vertical  chamber, 
30  ins.  or  more  in  diameter,  surrounded  by  a  great  number  of  tubes 


2" Feed 


Blow-off 


FIG.  102. — THE  WICKES  BOILEE. 

bent  nearly  to  the  form  of  a  short  U.  The  tubes  are  expanded  into 
the  central  shell,  and  are  placed  on  an  incline  so  that  one  end  is  about 
15  ins.  higher  than  the  other. 

The  boiler  is  self-contained,  no  brick  being  visible;  on  the  inside 
of  the  casing  is  a  terra-cotta  tile,  each  piece  being  fastened  by  a 
through-bolt  to  the  casing  so  that  any  section  of  the  boiler  can  be 
readily  taken  out,  brick  and  all,  without  disturbing  the  others,  to 
renew  tubes.  If  a  tube  should  need  renewing  the  defective  one  is  cut 


274  STEAM-BOILER  ECONOMY. 

out  and  a  stop-tube,  about  18  ins.  long,  with  a  welded  end,  is  inserted 
in  the  hole  from  the  inside  of  the  central  shell  and  expanded. 


FIG.  103.— MORRIN'S  CLIMAX  BOILER. 

Water-tube  Marine  Boilers. — Of  the  boilers  built  of  pipes  and 
fittings,  briefly  described  on  page  263,  the  Ward,  Roberts,  Almy  and 
Herreshoff  have  been  somewhat  extensively  used  in  steam-yachts  and 
torpedo-boats.  The  Belleville,  in  its  recent  forms,  has  come  largely 
into  use  in  the  French  mercantile  marine,  and  has  been  adopted  in 
several  ships  of  war,  including  large  cruisers,  in  the  British  Navy. 
For  descriptions  and  illustrations  of  many  other  forms  of  marine 
water-tube  boilers  see  Bertin  &  Robertson  on  "  Marine  Boilers "  and 


TYPES  OF  STEAM-BOILERS.  275 

AY.  S  Hutton  on  "Steam-Boiler  Construction."  Three  of  these  forms 
iire  described  below. 

The  Thornycroft  Boiler  (Fig.  104).  A  large  cylindrical  steam- 
•drum  is  connected  to  a  lower  water-drum  by  two  groups  of  curved 
generating  tubes  of  small  diam- 
eter. The  fire-grates  are  on  each 
side  of  the  water-drum.  The 
two  outer  rows  of  tubes  of  each 
group  are  brought  together,  mak- 
ing a  tube- wall,  but  so  as  to  leave 
openings  for  the  hot  gases  to  pass 
between  the  tubes  near  their  lower 
ends.  The  two  inner  rows  of  each 
group  are  in  like  manner  brought 
together,  except  near  their  upper 
ends,  where  there  are  passages  left 
between  them.  The  gases  thus  FIG.  104. — THORNYCROFT  BOILER. 
pass  from  the  combustion-chamber 

above  the  grates  on  each  side  into  the  flue  between  the  outer  and  inner 
tube-walls,  and  thence  into  the  heart-shaped  central  flue  which  leads 
to  the  funnel  at  the'back  of  the  boiler.  The  outer  sides  of  the  fire-box 
or  combustion- chamber  are  formed  by  tube-walls  leading  from  two  small 
water-drums  into  the  upper  part  of  the  steam-drum,  these  water- 
drums  being  connected  by  a  cross-pipe  at  the  back  of  the  boiler.  The 
generating  tubes  discharge  a  mingled  mass  of  steam  and  water  into 
the  steam-drum,  in  which  there  are  baffle-plates  to  separate  the 
steam  and  the  water.  The  steam  passes  into  an  internal  steam-pipe 
through  narrow  slits,  While  the  water  falls  to  the  bottom  of  the  steam- 
drum  and  is  thence  conveyed  by  large  central  return-pipes  to  the 
water-drum  at  the  bottom,  thus  insuring  a  rapid  circulation.  The 
following  data  of  a  large  Thornycroft  boiler  are  given  by  Hutton: 

Tube  surface sq.  ft.  4020 

Fire-grate  area., "    "    63.5 

Weight  of  the  boiler  and  mountings,  with  water tons  18$ 

Indicated  horse-power  on  trial,  with  triple-expansion  engines 2000 

"Working  pr  ssure  of  steam Ibs.  per  sq.  in.  220 

This  boiler  is  known  as  the  "Daring"  type.  Other  and  smaller 
toilers  of  the  Thornycroft  make  are  called  the  "Speedy"  and  the 
"  Launch  "  types.  The  Thornycroft  boiler  is  largely  used  in  torpedo- 
toats  and  high-speed  yachts,  especially  in  Great  Britain. 


276 


STEAM-BOILER  ECONOMY. 


The  Mosher  Boiler  (Fig.  105).  Two  steam-  and  water-drums  com- 
municate with  lower  water- chambers 
by  a  great  number  of  curved  tubes  of 
small  diameter,  and  also  by  two  ex- 
ternal down-take  tubes,  4  inches  in 
diameter.  The  front  and  back  cas- 
ings are  lined  with  fire-brick  covered 
with  asbestos,  and  the  upper  part 
with  a  layer  of  soap-stone  between" 
layers  of  asbestos.  This  boiler  is  used 
FIG.  105.— THE  MOSHER  BOILER,  in  many  high-speed  American  yachts. 

The  Babcock  &  Wilcox  Marine  Boiler  of  the  latest  form  is  shown 


FIG.  106. — LONGITUDINAL  SECTION  OF  BABCOCK  &  WILCOX  MARINE  WATER- 
TUBE  BOILER,  "  ALERT  "  TYPE,  SHOWING  SIDE  CASING  REMOVED. 


TYPES  OF  STEAM-BOILERS. 


277 


in  Fig.  106,  which  represents  one  of  the  boilers  of  the  U.  S.  cruiser 
Cincinnati.  This  boiler  has  been  extensively  adopted  in  the  British 
and  American  navies  for  the  largest  war-vessels,  and  since  1895  it  has 
been  used  with  great  success  in  the  Wilson  (British)  line  of  merchant 
steamers.  The  chief  features  in  which  it  differs  from  the  land  type 
of  the  Babcock  &  Wilcox  boiler,  Fig.  94,  page  26G,  have  been  designed 
for  the  purpose,  chiefly,  of  providing  a  very  large  area  of  grate  and 
hsating  surface,  together  with  relatively  small  weight  of  metal  and 
water  to  be  carried  in  the  contracted  space  allowed  in  ocean  steamers. 
The  tubes  in  the  lower  row  are  4  ins.  diameter,  all  the  others  being  2 
ins.  The  steam  and  water  drum  is  set  transversely  to  the  direction  of 
the  tubes.  The  fire-box  is  roofed  over  by  fire-brick  supported  by  the 
lower  row  of  tubes.  The  fire-door  is  placed  at  what  would  be  called 
the  rear  of  the  boiler  in  the  ordinary  land  boiler.  A  fuller  description 
of  this  boiler,  together  with  the  record  of  a  series  of  tests  made  by 
engineers  of  the  U.  S.  Navy  will  be  found  in  the  chapter  on  Results 
of  Steam-Boiler  Trials. 

Forms  of  Boiler  used  in  Different  Countries.— The  average  boiler- 
user  is  governed  in  his  selection  of  a  boiler  largely  by  local  custom  and 
prejudice,  and  therefore  different  forms  of  boiler  are  the  favorites  in 
different  parts  of  the  world.  To  show  how  generally  this  is  true,  we 
have  the  following  figures  showing  the  percentage  of  various  types  of 
boilers  used  in  Great  Britain,  France,  Germany,  Switzerland,  and 
Austria,  prepared  by  Mr.  Hiller,  of  the  National  Boiler  Insurance  Co., 
of  Manchester,  England,  and  given  by  Mr.  R.  S.  Hale  in  Circular  No. 
5,  1896,  of  the  Steam  Users'  Association,  Boston,  Mass.: 

PER   CENT   OF   BOILERS    OF   VARIOUS    TYPES   USED    IN    EUROPE. 


1895. 

1893-4. 

Austria. 

United 
Kingdom. 

France. 

Germany. 

Switzer- 
land. 

Lancashire  and  similar  types.  . 
Cornish  and  similar  types  .  .  . 
Externally  fired  cylindrical.  .  . 
Externally  fired  multitubular. 

38.0 
23.7 
f6.8 

ii!6 

16.6 
1.8 
2.1 

4.7 
8.2 
57.3 
13.4 
5.1 
3.6 
5.7 
2.0 

357 
15.3 
14.8 
5.2 
17.3 
5.0 
4.6 
2.1 

19.6 

40.8 
15.5 
3.5 
5  7 
13.5 
1.4 

* 
* 

41.0 
7.5 
10.5 
6.1 
3.8 
1.4 

*  Lancashire,  Cornish,  and  similar  types,  29.7.        t  Including  "  elephant  "  boilers. 

We  note  from  this  table  that  the  Lancashire,  Cornish,  and  similar 
types  form  a  majority  of  all  the  boilers  in  the  United  Kingdom,  Ger* 


278  STEAM-BOILER  ECONOMY. 

many,  and  Switzerland;  that  the  externally  fired  cylindrical,  including" 

the  elephant  boilers,  are  in  the  lead  in  France  and  Austria,  and  that 
the  externally  fired  multitubular  boiler,  which  is  the  most  common 
boiler  in  the  United  States,  does  not  appear  to  be  used  at  all  in  Great 
Britain,  and  but  to  a  small  extent  in  other  European  countries.  If 
the  table  had  included  boilers  in  the  United  States,  it  would  probably 
put  the  externally  fired  multitubular  boilers  far  in  the  lead  of  all  the 
others,  the  elephant,  the  Cornish,  and  the  Lancashire  boilers  would 
not  appear  at  all,  the  externally  fired  cylindrical  boilers  to  probably 
less  than  5  per  cent,  the  small  verticals  would  probably  have  a  larger 
percentage  than  in  any  country  in  Europe,  large  verticals,  such  as  the 
Manning,  which  are  not  named  in  the  European  list,  would  appear 
with  a  small  percentage,  and  water-tube  boilers  would  probably  have 
a  higher  percentage  than  anywhere  in  Europe. 

It  must  be  said  in  relation  to  this  table,  that  it  is  not  fairly  repre- 
sentative of  European  practice  in  the  purchase  of  new  boilers  at  the 
present  date,  but  is  simply  the  percentage  of  boilers  in  use  in  1895,  in- 
cluding both  old  and  new;  many  of  them  are  no  doubt  forty  years 
old,  or  more.  If  a  table  were  prepared  of  the  percentages  of  boilers  of 
various  types  now  sold,  it  would  undoubtedly  show  a  much  higher 
percentage  of  water-tube  boilers,  which  have  within  the  last  ten  years 
become  very  common  in  Belgium,.  France,  and  Germany,  and  are 
rapidly  increasing  in  favor  in  England  as  well  as  in  the  United  States. 

There  is  nothing  in  the  steam-engine  practice  of  different  countries,, 
nor  in  the  character  of  fuel,  or  of  water  used,  which  will  account  for 
the  great  difference  in  boiler  practice  in  the  different  countries, 
and  the  only  explanation  of  it  appears  to  be  local  custom,  prejudice, 
and  conservatism.  The  difference  between  American  and  European 
practice  may  be  partly  explained  by  financial  considerations.  In. 
England,  where  manufacturing  establishments  are  generally  of  many 
years'  standing  and  provided  with  abundant  capital,  and  where  the 
interest  on  money  is  low,  the  first  cost  of  a  boiler-plant  is  usually  a 
consideration  of  secondary  importance.  This  has  led  to  the  general 
introduction  of  the  Lancashire  boiler,  which  is  very  high  in  first  cost. 
In  America,  where  most  of  the  manufacturing  concerns  have  grown 
from  small  beginnings,  where  capital  for  investment  in  manufacturing 
has  been  scarce  and  interest  high,  low  first  cost  has  been  considered 
of  chief  importance,  and  on  this  account  the  horizontal  multitubular 
boiler,  which  is  almost  unknown  in  England,  has  come  into  most  ex- 
tensive use.  In  recent  years,  however,  in  the  United  States,  the  in- 
crease of  wealth,  the  decrease  of  the  rate  of  interest,  the  growth  of 


TYPES  OF  STEAM-BOILERS.  279 

manufacturing  concerns  into  establishments  of  vast  extent  and  abund- 
ant capital,  the  decrease  of  the  margin  of  profit  in  manufactured 
goods,  and  intense  competition,  have  all  tended  to  bring  about  changes 
in  the  ideas  and  methods  of  manufacturers  and  other  steam-users. 
They  are  now  disposed  to  look  more  carefully  into  the  questions  of  econ- 
omy of  fuel  and  of  durability  of  steam-boilers,  and  are  more  willing 
than  formerly  to  try  boilers  of  higher  first  cost  if  they  can  be  assured 
of  an  ultimate  saving  in  annual  expense. 


CHAPTER  XL 

BOILER   HORSE-POWER— PROPORTIONS  OF  HEATING  AND   GRATE 
SURFACE— PERFORMANCE  OF  BOILERS. 

The  Horse-power  of  a  Steam-boiler, — The  term  ' ( horse-power  "  has 
two  meanings  in  engineering:  First,  an  absolute  unit  or  measure  of  the 
rate  of  work;  that  is,  of  the  work  done  in  a  certain  definite  period  of 
time,  by  a  source  of  energy,  as  a  steam-boiler,  a  waterfall,  a  current 
of  air  or  of  water,  or  by  a  prime  mover,  as  a  steam-engine,  a  water- 
wheel,  or  a  wind-mill.  The  value  of  this  unit,  whenever  it  can  be 
expressed  in  foot-pounds  of  energy,  as  in  the  case  of  steam-engines, 
water-wheels,  and  waterfalls,  is  33,000  foot-pounds  per  minute.  In 
the  case  of  boilers,  where  the  work  done,  the  conversion  of  water  into 
steam,  cannot  be  expressed  in  foot-pounds  of  available  energy,  the 
usual  value  given  to  the  term  horse-power  is  the  evaporation  of  30  Ibs. 
of  water  of  a  temperature  of  100°  F.  into  steam  at  70  Ibs.  pressure  above 
the  atmosphere.  Both  of  these  units  are  arbitrary;  the  first,  33,000 
foot-pounds  per  minute,  originally  used  by  James  Watt,  being  con- 
sidered equivalent  to  the  power  exerted  by  a  good  London  draft- 
horse,  and  the  second,  30  Ibs.  of  water  evaporated  per  hour,  being  con- 
sidered to  be  the  steam  requirement  per  indicated  horse-power  of  an 
average  engine. 

The  second  definition  of  the  term  horse-power  is  an  approximate 
measure  of  the  size,  capacity,  value,  or  "rating"  of  a  boiler,  engine, 
water-wheel,  or  other  source  or  conveyer  of  energy,  by  which  measure 
it  may  be  described,  bought  and  sold,  advertised,  etc.  No  definite 
value  can  be  given  to  this  measure,  which  varies  largely  with  local 
custom  or  individual  opinion  of  makers  and  users  of  machinery.  The 
nearest  approach  to  uniformity  which  can  be  arrived  at  in  the  term 
"horse-power,"  used  in  this  sense,  is  to  say,  that  a  boiler,  engine, 
water-wheel,  or  other  machine,  "rated"  at  a  certain  horse-power, 
should  be  capable  of  steadily  developing  that  horse-power  for  a  long 
period  of  time  under  ordinary  conditions  of  use  and  practice,  leaving 
to  local  custom,  to  the  judgment  of  the  buyer  and  seller,  to  written 

280 


BOILER  HORtE-POWER.  281 

contracts  of  purchase  and  sale,  or  to  legal  decisions  upon  sucli  con- 
tracts, the  interpretation  of  what  is  meant  by  the  term  "ordinary 
conditions  of  use  and  practice.''  (Trans.  A.  S.  M.  E.,  vol.  vii.  p.  226.) 
Definitions  of  "Boiler  Horse-power." — The  question  of  denning 
the  '-commercial"  horse-power  of  a  steam-boiler  was  considered  by 
the  two  committees  on  steam-boiler  trials  (1885  and  1899)  of  the 
American  Society  of  Mechanical  Engineers.*  The  second  committee 
(18!;9)  reported  on  this  subject  as  follows  : 

The  Committee  recommends  that,  as  far  as  possible,  the  capacity 
of  a  boiler  be  expressed  in  terms  of  the  "number  of  pounds  of  water 
evaporated  per  hour  from  and  at  212  degrees."  It  does  not  seem  ex- 
pedient, however,  to  abandon  the  widely-recognized  measure  of  capac- 
ity of  stationary  or  land  boilers  expressed  in  terms  of  "  boiler  horse- 
power." 

The  unit  of  commercial  boiler  horse-power  adopted  by  the  Com- 
mittee of  1885  was  the  same  as  that  used  in  the  reports  of  the  boiler- 
tests  made  at  the  Centennial  Exhibition  in  1876.  The  Committee  of 
1885  reported  in  favor  of  this  standard  in  language  of  which  the  fol- 
lowing is  an  extract : 

Your  Committee,  after  due  consideration,  has  determined  to  ac- 
cept the  Centennial  standard,  and  to  recommend  that  in  all  standard 
trials  the  commercial  horse-power  be  taken  as  an  evaporation  of  30 
pounds  of  water  per  hour  from  a  feed-water  temperature  of  100  de- 
grees Fahr.  into  steam  at  70  pounds  gauge-pressure,  which  shall  be 
considered  to  be  equal  to  34^  units  of  evaporation ;  that  is,  to  34^ 
pounds  of  water  evaporated  from  a  feed-water  temperature  of  212  de- 
grees Fahr.  into  steam  at  the  same  temperature.  This  standard  is 
equal  to  33,305  thermal  units  per  hour. 

The  Committee  of  1899  accepted  the  same  standard,  but  reversed 
the  order  of  two  clauses  in  the  statement,  and  slightly  modified  them, 
so  as  to  read  as  follows  : 

The  unit  of  commercial  horse-power  developed  by  a  boiler  shall  be 
fcaken  as  34^  units  of  evaporation  per  hour  ;  that  is,  34^  pounds  of 
water  evaporated  per  hour  from  a  feed-water  temperature  of  212  de- 
grees Fahr.  into  dry  steam  of  the  same  temperature.  This  standard 
is  equivalent  to  33,317  British  thermal  units  per  hour.  It  is  also 
practically  equivalent  to  an  evaporation  of  30  pounds  of  water  from  a 
feed-water  temperature  of  100  degrees  Fahr.  into  steam  at  70  pounds 
gauge-pressure,  f 

*  Trans.  A.  S.  M.  E.,  vols.  vi.  and  xxi. 

f  According  to  the  tables  in  Porter's  Treatise  on   tlie  Richards'  Steam-engine 
Indicator,  an  evaporation  of  30  pounds  of  water  from  100  degrees  Fahr.  into  steam, 


282  STEAM-BOILER  ECONOMY. 

The  Committee  also  indorsed  the  statement  of  the  Committee  of 
1885  concerning  the  commercial  rating  of  boilers,  changing  somewhat 
its  wording,  so  as  to  read  as  follows  : 

A  boiler  rated  at  any  stated  capacity  should  develop  that  capacity 
when  using  the  best  coal  ordinarily  sold  in  the  market  where  the  boiler 
is  located,  when  fired  by  an  ordinary  fireman,  without  forcing  the  fires, 
while  exhibiting  good  economy  ;  and  further,  the  boiler  should  develop 
at  least  one-third  more  than  the  stated  capacity  when  using  the  same 
fuel  and  operated  by  the  same  fireman,  the  full  draft  being  employed 
and  the  fires  being  crowded  ;  the  available  draft  at  the  damper,  unless 
otherwise  understood,  being  not  less  than  -J  inch  water-column. 

Measures  for  Comparing  the  Duty  of  Boilers, — The  measure  of 
the  efficiency  of  a  boiler  is  the  number  of  pounds  of  water  evaporated 
per  pound  of  combustible,  the  evaporation  being  reduced  to  the 
standard  of  "  from  and  at  212°  "  ;  that  is,  the  equivalent  evaporation 
from  feed-water  at  a  temperature  of  212°  F.  into  steam  at  the  same 
temperature. 

The  measure  of  the  capacity  of  a  boiler  is  the  number  of  pounds  of 
water  evaporated  from  and  at  212°  F.  per  hour,  or  it  is  the  amount  of 
" boiler  horse-power"  developed,  a  horse-power  being  defined  as  the 
evaporation  of  34|  Ibs.  of  water  per  hour  from  and  at  212°. 

The  measure  of  relative  rapidity  of  steaming  of  boilers  is  the  num- 
ber of  pounds  of  water  evaporated  from  and  at  212°  per  hour  per  square 
foot  of  water-heating  surface. 

The  measure  of  relative  rapidity  of  combustion  of  fuel  in  boiler- 
furnaces  is  the  number  of  pounds  of  coal  burned  per  hour  per  square 
foot  of  grate  surface. 

Proportions  of  Grate  and  Heating  Surface  required  for  a  given 
Commercial  Horse-power.— (1  H.P.  =  34.5  Ibs.  from  and  at  212°  F.) 

Average  proportions  for  maximum  economy  for  land  boilers  fired 
with  good  anthracite  coal : 

Heating  surface  per  horse-power 11.5  sq.  ft. 

Grate  "          "  "  1/3      " 

Ratio  of  beating  to  grate  surface 34.5      " 

Water  evap'd  from  and  at  212°  per  sq.  ft.  H.  S.  per  hour    3     Ibs. 
Combustible  burned  per  H.  P.  per  hour 3       " 

at  70  pounds  pressure  is  equal  to  an  evaporation  of  34,488  pounds  from  and  at  212 
degrees  ;  and  an  evaporation  of  34£  pounds  from  and  at  212  degrees  Fahr.  is  equal 
to  30,010  pounds  from  100  degrees  Fahr.  into  steam  at  70  pounds  pressure. 

The  "unit  of  evaporation  "  being  equivalent  to  965.7  thermal  units,  the  conir 
mercial  horse  power  =  34.5  X  965.7  =  33,317  thermal  units. 


BOILER  HORSE-POWER.  283 

Coal  with  1/6  refuse,  Ibs.  per  H.  P.  per  hour 3.6  Ibs. 

Combustible  burned  per  sq.  ft.  grate  per  hour 9       " 

Coal  with  1/6  refuse,  Ibs.  per  sq.  ft.  grate  per  hour 10.8    " 

Water  evap'd  from  and  at  212°  per  Ib.  combustible 11.5    " 

"       "     "    "      "     "    coal  (1/6  refuse)..     9.6    " 

Heating  Surface. — For  maximum  economy  with  any  kind  of  fuel  a 
boiler  should  be  proportioned  so  that  at  least  one  square  foot  of  heat- 
ing surface  should  be  given  for  every  3  Ibs.  of  water  to  be  evaporated 
from  and  at  212°  i\  per  hour.  Still  more  liberal  proportions  are  re- 
quired if  a  portion  of  the  heating  surface  has  its  efficiency  reduced  by: 
1.  Tendency  of  the  heated  gases  to  short-circuit;  that  is,  to  select  pas- 
sages of  least  resistance  and  flow  through  them  with  high  velocity,  to 
the  neglect  of  other  passages.  2.  Deposition  of  soot  from  smoky 
fuel.  3.  Incrustation.  If  the  heating  surfaces  are  clean,  and  the- 
heated  gases  pass  over  them  uniformly,  little  if  any  increase  in  economy 
can  be  obtained  by  increasing  the  heating  surface  beyond  the  propor- 
tion of  1  sq.  ft.  to  every  3  Ibs..  of  water  to  be  evaporated,  and  with  all 
conditions  favorable  but  little  decrease  of  economy  will  take  place  if 
the  proportion  is  1  sq.  ft.  to  every  4  Ibs.  evaporated  ;  but  in  order  to 
provide  for  driving  of  the  boiler  beyond  its  rated  capacity,  and  for 
possible  decrease  of  efficiency  due  to  the  causes  above  named,  it  is 
better  to  adopt  1  sq.  ft.  to  3  Ibs.  evaporation  per  hour  as  the  mini- 
mum standard  proportion. 

Where  economy  may  be  sacrificed  to  capacity,  as  where  fuel  is  very 
cheap,  it  is  customary  to  proportion  the  heating  surface  much  less  lib- 
erally. The  following  table  shows  approximately  the  relative  results 
that  may  be  expected  with  different  rates  of  evaporation,  with  anthra- 
cite coal: 

Lbs.  water  evaporated  from  and  at  212°  per  sq.  ft.  heating  surface  per  hour  : 

2          2.5  3          3.5  4  5  6  7  89          10 

Sq.  ft.  heating  surface  required  per  horse-power  : 
17.3         13.8       11.5          9.8         8.6        6.8        5.8         4.9        4.3         3.8        3.5 

Ratio  of  heating  to  grate  surface  if  £  sq.  ft.  of  G.  S.  is  required  per  H.P.  : 
52        41.4       34.5         29.4       25.8      20.4      17.4       13.7      12.9       11.4      10.5 

Probable  relative  economy  : 
100          100         99  98          95         92         88          84         80          75         70 

Probable  temperature  of  chimney-gases,  degrees  F.  : 
450          450        470          490         520       580       650        710       770        850       930 

The  relative  economy  will  vary  not  only  with  the  amount  of  heat- 
ing surface  per  horse-power,  but  with  the  efficiency  of  that  heating 
surface  as  regards  its  capacity  for  transfer  of  heat  from  the  heated  gases 


28 i  STEAM-BOILER  ECONOMY. 

to  the  water,  which  will  depend  on  its  freedom  from  soot  and  incrus- 
tation, and  upon  the  circulation  of  the  water  and  the  heated  gases. 

With  bituminous  coal  the  efficiency  will  largely  depend  upon  the 
thoroughness  with  which  the  combustion  is  effected  in  the  furnace. 

The  efficiency  with  any  kind  of  fuel  will  greatly  depend  upon  the 
amount  of  air  supplied  to  the  furnace  in  excess  of  that  required  to 
support  combustion.  With  strong  draft  and  thin  fires  this  excess  may 
be  very  great,  causing  a  serious  loss  of  economy.  This  subject  has 
been  fully  discussed  in  Chapter  IX. 

Measurement  of  Heating  Surface. — Authorities  are  not  agreed  as 
to  the  methods  of  measuring  the  heating  surface  of  steam-boilers.  The 
usual  rule  is  to  consider  as  heating  surface  all  the  surfaces  that  are 
surrounded  by  water  on  one  side  and  by  flame  or  heated  gases  on  the 
other. 

It  has  hitherto  been  the  common  practice  of  boiler-makers  to  con- 
side-r  all  surfaces  as  heating  surfaces  which  transmit  heat  from  the 
flame  or  gases  to  the  water,  making  no  allowance  for  different  degrees 
of  effectiveness  ;  also,  to  use  the  external  instead  of  the  internal 
diameter  of  tubes,  for  greater  convenience  in  calculation,  the  external 
diameter  of  boiler-tubes  usually  being  made  in  even  inches  or  half 
inches.  This  method,  however,  is  inaccurate  in  the  case  of  a  fire- 
tube  boiler,  for  the  true  heating  surface  of  a  fire-tube  is  the  side  ex- 
posed to  the  hot  gases,  i.e.,  the  inner  surface.  The  resistance  to  the 
passage  of  heat  from  the  hot  gases  on  one  side  of  a  tube  or  plate  to 
the  water  on  the  other  consists  almost  entirely  of  the  resistance  to  the 
passage  of  the  heat  from  the  gases  into  the  metal,  the  resistance  of  the 
metal  itself  and  that  of  the  wetted  surface  being  practically  nothing.* 

RULE  for  finding  the  heating  surface  of  horizontal  tubular  boilers: 
Take  the  dimensions  in  inches.  Multiply  two-thirds  of  the  circum- 
ference of  the  shell  by  its  length;  multiply  the  sum  of  the  circum- 
ferences of  all  the  tubes  by  their  common  length;  to  the  sum  of  these 
products  add  two-thirds  of  the  area  of  both  tube-sheets;  from  this  sum 
subtract  twice  the  combined  area  of  all  the  tubes;  divide  the  remainder 
by  144  to  obtain  the  result  in  square  feet. 

RULE  for  finding  the  heating  surface  of  vertical  tubular  boilers: 
Multiply  the  circumference  of  the  fire-box  (in  inches)  by  its  height 
above  the  grate;  multiply  the  combined  circumference  of  all  the  tubes 
by  their  length,  and  to  these  two  products  add  the  area  of  the  lower 

*S*e  paper  by  C.  W.  Baker,  Trans.  A.  S.  M.  E.,  vol.  xix.  p.  571. 


BOILER  IIORzE-POWER.  285 

tube-sheet;  from  this  sum  subtract  the  area  of  all  the  tubes,  and  divide 
by  144  :  the  quotient  is  the  number  of  square  feet  of  heating  surface. 

RULE  for  finding  the  square  feet  of  heating  surface  in  tubes:  Multi- 
ply the  number  of  tubes  by  the  diameter  of  a  tube  in  inches,  by  its 
length  in  feet,  and  by  .2618. 

Horse-power,  Builder's  Rating.  Heating  Surface  per  Horse-power. 
—It  is  a  general  practice  among  builders  to  furnish  from  10  to  12 
square  feet  of  heating  surface  per  horse-power,  but  as  the  practice  is 
not  uniform,  bids  and  contracts  should  always  specify  the  amount  of 
heating  surface  to  be  furnished.  Not  less  than  one-third  square  foot 
of  grate  surface  should  ordinarily  be  furnished  per  horse-power  in  order 
that  the  boiler  may  be  able  to  develop  from  30  to  50  per  cent  more 
than  its  stated  power  for  short  periods  in  emergencies;  but  a  smaller 
proportion  may  be  sufficient  with  free-burning  coal  and  strong  draft. 
See  "  Grate  Surface,"  below. 

Engineering  News,  July  5,  1894,  gives  the  following  rough-and- 
ready  rule  for  finding  approximately  the  commercial  horse-power  of 
tubular  or  water-tube  boilers:  Number  of  tubes  X  their  length  in  feet 
X  their  nominal  diameter  in  inches  ~  50  —  nLd  -f-  50.  The  nuni- 


.  nLd 

her  of  square  feet  or  surface  in  the  tubes  is  —  r^r—  =  TTTTJ  auci  the  horse- 

L6  O.b2 

power  at  12  square  feet  of  surface  of  tubes  per  horse-power,  not  count- 
ing the  shell,  =  nLd  -f-  45.8.  If  15  square  feet  of  surface  of  tubes  be 
taken,  it  is  nLd  -=-  57.3.  Making  allowance  for  the  heating  surface 
in  the  shell  will  reduce  the  divisor  to  about  50. 

Horse-power  of  Marine  and  Locomotive  Boilers.  —  The  term  horse- 
power is  not  generally  used  in  connection  with  boilers  in  marine  prac- 
tice, or  with  locomotives.  The  boilers  are  designed  to  suit  the  engines, 
and  are  rated  by  extent  of  grate  and  heating  surface  only. 

Grate  Surface.  —The  amount  of  grate  surface  required  per  horse- 
power, and  the  proper  ratio  of  heating  surface  to  grate  surface  are  ex- 
tremely variable,  depending  chiefly  upon  the  character  of  the  coal  and 
upon  the  rate  of  draft.  With  good  coal,  low  in  ash,  approximately 
equal  results  may  be  obtained  with  large  grate  surface  and  light  draft 
and  with  small  grate  surface  and  strong  draft,  the  total  amount  of 
coal  burned  per  hour  being  the  same  in  both  cases.  With  good 
bituminous  coal,  like  Pittsburg,  low  in  ash,  the  best  results  apparently 
are  obtained  with  strong  draft  and  high  rates  of  combustion,  pro- 
vided the  grate  surfaces  are  cut  down  so  that  the  total  coal  burned  per 
hour  is  not  too  great  for  the  capacity  of  the  heating  surface  to  absorb 
the  heat  produced. 


286 


STEAM-BOILER  ECONOMY. 


With  coals  high  in  ash,  especially  if  the  ash  is  easily  fusible,  tend- 
ing to  choke  the  grates,  large  grate  surface  and  a  slow  rate  of  com- 
bustion are  required,  unless  means,  such  as  shaking-grates,  are  pro- 
vided to  get  rid  of  the  ash  as  fast  as  it  is  made. 

The  amount  of  grate  surface  required  per  horse-power  under  vari- 
ous conditions  may  be  estimated  from  the  following  table : 


£«  - 

-gftjl 

Pounds  of  Coal  burned  per  square  foot  of  Grate 

*§*?!" 

I« 

per  hour. 

j§£3£.8 

ja& 

8 

10 

12    1   15 

20 

25 

30 

35 

40 

Sq.  Ft.  Grate  per  H.P. 

Good  coal 

j    10 

3.45 

.43 

.35 

.28 

.23 

.17 

.14 

.11 

.10    .09 

and  boiler, 

i  9 

3.83 

.48 

.38 

.32 

.25 

.19 

.15 

.13 

.11 

.10 

Fair   coal    or 
boiler, 

(      8.61 

1      8 
(      7 

4 
4.31 
4.93 

.50 
.54 
.62 

.40 
.43 
.49 

.33 
.36 
.41 

.26 
.29 
.33 

,20 
.22 
.24 

.16 
.17 
.20 

.13 
.14 
.17 

.12 
.13 
.14 

.10 

.11 

.12 

Poor    coal   or 

I      6.9 

5 

.63 

.50   .42 

.34 

.25 

.20 

.17 

.15 

.13 

boiler 

1      6 

5.75 

.72 

.58   .48 

.38 

.29 

.23 

.19 

.17 

.14 

(      5 

6.9 

.86 

.69 

.58 

.46 

.35 

.28 

.23 

.22 

.17 

Lignite  and 
poor  boiler, 

|      3.45 

10 

1.25 

1.00 

.83 

.67 

.50 

.40 

.33 

.29 

.25 

In  designing  a  boiler  for  a  given  set  of  conditions,  the  grate  surface 
should  be  made  as  liberal  as  possible,  say  sufficient  for  a  rate  of  com- 
hustion  of  10  Ibs.  per  square  foot  of  grate  for  anthracite,  and  15  Ibs. 
per  square  foot  for  bituminous  coal,  and  in  practice  a  portion  of  the 
grate  surface  may  be  bricked  over  if  it  is  found  that  the  draft,  fuel,  or 
other  conditions  render  it  advisable.  In  earlier  times,  when  plain 
cylinder  and  two-flue  boilers  were  in  common  use,  it  was  customary 
to  have  a  ratio  of  say  1  to  20,  or  1  to  25,  of  grate  heating  surface. 
With  very  slow  rates  of  combustion  these  proportions  gave  a  fair  degree 
of  economy,  but  as  boilers  were  driven  faster,  the  economy  fell  off,  and 
the  loss  of  heat  in  the  chimney-gases  became  excessive.  This  was  cor- 
rected by  the  introduction  of  horizontal  tubular  boilers,  in  which  the 
grate  surface  remaining  the  same,  the  extent  of  heating  surface  was  in- 
creased until  the  ratio  of  grate  to  heating  surface  became  1  to  30.  When 
water-tube  boilers  came  largely  into  use  it  was  found  that  the  highest 
economy  could  be  obtained  with  a  ratio  of  1  to  40  or  1  to  50.  In 
recent  years  it  has  become  quite  common  to  pile  up  heating  surface  on 
a  given  area  of  grate,  so  that  ratios  of  1  to  60  are  not  infrequent.  The 
evident  advantage  of  such  a  ratio  is  that  it  enables  a  given  horse-power 
to  be  built  on  a  smaller  ground-space  than  before,  and  by  using  tubes  18 


BOILER  HORSE-POWER.  287 

feet  long  instead  of  14,  and  piling  tubes  10  or  15  rows  high  instead  of 
7  or  8,  the  first  cost  of  a  given  horse-power  is  reduced.  With  anthra- 
cite egg  coal,  or  with  semi-bituminous  coal  low  in  ash,  and  with  a  strong 
draft,  no  disadvantage  results  from  this  method  of  construction;  but 
with  poorer  coals,  such  as  pea,  buckwheat,  and  rice,  and  the  bituminous 
coals  of  Western  States,  high  in  moistm*e,  sulphur,  and  ash,  there  is  a 
most  serious  disadvantage,  namely,  that  of  cutting  down  the  working 
•capacity  of  the  boiler.  A  water-tube  boiler  with  3300  sq.  ft.  of  heating 
surface  and  46  sq.  ft.  of  grate  surface,  having  a  ratio  of  50  to  1,  and  rated 
at  200  H.P.,  may  easily  be  driven  with  semi-bituminous  or  with  Pitts- 
burg  coal,  the  draft  being  sufficient,  to  over  300  H.P.,  while  with  a 
poor  grade  of  Illinois  coal,  or  with  buckwheat  anthracite,  it  would  be 
difficult  to  drive  the  boiler  up  to  its  rating.  With  ordinary  grates  and 
hand-firing  with  such  coals,  increasing  the  draft  beyond  a  certain 
amount  does  not  increase  the  coal-burning  capacity,  for  rapid  driving 
only  causes  the  ash  to  accumulate  more  rapidly  and  to  fuse  into  clinker, 
choking  the  draft  through  the  coal  arid  necessitating  frequent  clean- 
ing. Shaking-grates  may  remedy  the  trouble  to  some  extent,  but 'the 
best  remedy  is  an  increase  of  the  area  of  grate  surface  and  a  slower 
rate  of  combustion. 

In  drawing  specifications  for  bids  upon  boilers  it  is  quite  as  essen- 
tial that  the  extent  of  grate  surface  should  be  specified  as  the  extent 
of  heating  surface,  especially  when  the  coal  to  be  used  is  of  a  poor 
quality.  When  two  competing  boilermakers  offer  boilers  of  the  same 
type  and  the  same  extent  of  heating  surface,  that  one  should  be  pre- 
ferred, other  things  being  equal,  wrhich  has  the  larger  grate  surface. 
It  may  be  driven  to  a  greater  capacity  than  the  other,  to  meet  emer- 
gencies, or  it  will  give  the  same  capacity  with  a  poor  grade  of  coal  that 
the  other  will  give  with  better  coal.  Too  large  a  grate  surface  is  an 
evil  that  may  easily  be  remedied,  by  shortening  the  grates,  but  too 
small  grate  surface  necessitates  the  use  of  the  higher  priced  coals,  en- 
tails more  labor  in  handling  fires,  more  frequent  cleaning  of  fires,  and 
consequent  loss  of  economy. 

Boilers  are  usually  sold  on  the  basis  of  rated  horse-power,  from  10 
to  12  square  feet  of  heating  surface  being  taken  as  equivalent  to  a 
horse-power,  but  of  two  boilers,  each  of  the  same  rating  on  this  basis, 
but  one  having  say  40  sq.  ft.  of  grate  and  the  other  60,  the  latter, 
with  a  poor  grade  of  coal,  will  develop  almost  50  per  cent  greater 
power  than  the  former  and  will  give  almost  the  same  economy.  With 


288  STEAM-BOILER  ECONOMY. 

a  free -burn  ing  coal,  low  in  ash,  and  ample  draft,  the  boiler  with  40  sq. 
ft.  of  grate  may  develop  30  or  40  per  cent  above  its  rating,  and  the 
one  with  60  sq.  ft.  nearly  100  per  cent  above  rating,  but  in  this  case, 
the  boiler  with  large  grate  surface  will  show  a  great  loss  of  economy, 
because  it  is  overdriven. 

Proportions  of  Areas  of  Flues  and  other  Gas-passages. — Eules  are 
sometimes  given  making  the  area  of  gas-passages  bear  a  certain  ratio 
to  the  area  of  the  grate  surface;  thus  a  common  rule  for  horizontal 
tubular  boilers  is  to  make  the  area  over  the  bridge  wall  -\  of  the  grate 
surface,  the  flue  area  -|-,  and  chimney  area  -J-. 

For  average  conditions  with  anthracite  coal  and  moderate  draft, 
say  a  rate  of  combustion  of  12  Ibs.  coal  per  square  foot  of  grate  per 
hour,  and  a  ratio  of  heating  to  grate  surface  of  30  to  1,  this  rule  is  as 
good  as  any,  but  it  is  evident  that  if  the  draft  were  increased  so  as 
to  cause  a  rate  of  combustion  of  24  Ibs.,  requiring  the  grate  surface  to 
be  cut  down  to  a  ratio  of  60  to  1,  the  areas  of  gas-passages  should  not 
be  reduced  in  proportion.  The  amount  of  coal  burned  per  hour  being 
the  same  under  the  changed  conditions,  and  there  being  no  reason 
why  the  gases  should  travel  at  a  higher  velocity,  the  actual  areas  of  the 
passages  should  remain  as  before,  but  the  ratio  of  the  area  to  the  grate 
surface  would  in  that  case  be  doubled. 

Mr.  Barrus  states  that  the  highest  efficiency  with  anthracite  coal  is 
obtained  when  the  tube  area  is  ^  to  -^0-  of  the  grate  surface,  and 
with  bituminous  coal  when  it  is  |  to  -*-,  for  the  conditions  of  medium 
rates  of  combustion,  such  as  10  to  12  Ibs.  per  square  foot  of  grate  per 
hour,  and  12  square  feet  of  heating  surface  allowed  to  the  horse-power. 

The  tube  area  should  be  made  large  enough  not  to  choke  the 
draft,  and  so  lessen  the  capacity  of  the  boiler;  if  made  too  large  the 
gases  are  apt  to  select  the  passages  of  least  resistance  and  escape  from 
them  at  a  high  velocity  and  high  temperature. 

This  condition  is  very  commonly  found  in  horizontal  tubular 
boilers  where  the  gases  go  chiefly  through  the  upper  rows  of  tubes; 
sometimes  also  in  vertical  tubular  boilers,  where  the  gases  are  apt  to 
pass  most  rapidly  through  the  tubes  nearest  to  the  centre.  It  may  to 
some  extent  be  remedied  by  placing  retarders  in  those  tubes  in  which 
the  gases  travel  the  quickest. 

Air-passages  Through  Grate-bars. — The  usual  practice  is  to  make 
the  air-opening  equal  to  30$  to  50$  of  the  area  of  the  grate;  the 
larger  the  better,  to  avoid  stoppage  of  the  air-supply  by  clinker;  but, 


BOILER  HORSE-POWER. 

•with  coal  free  from  clinker,  much  smaller  air-space  may  be  used  with- 
out detriment.  See  "  Grate-bars,"  in  Chap.  VII.  page  151. 

Performance  of  Boilers. — The  performance  of  a  steam-boiler  com- 
prises both  its  capacity  for  generating  steam  and  its  economy  of  fuel. 
Capacity  depends  upon  size,  both  of  grate  surface  and  of  heating 
^surface,  upon  the  kind  of  coal  burned,  upon  the  draft,  and  also  upon 
the  economy.  Economy  of  fuel  depends  upon  the  completeness  with 
which  the  coal  is  burned  in  the  furnace,  upon  the  proper  regulation  of 
the  air-supply  to  the  amount  of  coal  burned,  and  upon  the  thorough- 
ness with  which  the  boiler  absorbs  the  heat  generated  in  the  furnace. 
The  absorption  of  heat  depends  upon  the  extent  of  heating  surface  in 
relation  to  the  amount  of  coal  burned  or  of  water  evaporated,  upon 
the  arrangement  of  the  gas-passages,  and  upon  the  cleanness  of  the 
surfaces.  The  capacity  of  a  boiler  may  increase  with  increase  of 
economy  when  this  is  due  to  more  thorough  combustion  of  the  coal  or 
to  better  regulation  of  the  air-supply,  or  it  may  increase  at  the  expense 
of  economy  when  the  increased  capacity  is  due  to  overdriving,  causing 
an  increased  loss  of  heat  in  the  chimney-gases.  The  relation  of 
capacity  to  economy  is  therefore  a  complex  one,  depending  on  many 
variable  conditions. 

Many  attempts  have  been  made  to  construct  a  formula  expressing 
the  relation  between  capacity,  rate  of  driving,  or  evaporation  per 
square  foot  of  heating  surface,  to  the  economy,  or  evaporation  per 
pound  of  combustible;  but  none  of  them  can  be  considered  satisfactory, 
since  they  make  the  economy  depend  only  on  the  rate  of  driving  (a 
few  so-called  " constants,"  however,  being  introduced  in  some  of  them 
for  different  classes  of  boilers,  kinds  of  fuel,  or  kind  of  draft),  and 
fail  to  take  into  consideration  the  numerous  other  conditions  upon 
which  economy  depends.  Such  formulae  are  Rankine's,  Clark's, 
Emery's,  Isherwood's,  Carpenter's,  and  Bale's.  A  discussion  of  them 
all  may  be  found  in  Mr.  R.  S.  Hale's  paper  on  "  Efficiency  of  Boiler 
Heating  Surface,"  in  Trans.  Am.  Soc.  M.  E.,  vol.  xviii.  p.  328.  Mr. 
Hale's  formula  takes  into  account  the  effect  of  radiation,  which  re- 
duces the  economy  considerably  when  the  rate  of  driving  is  less  than 
3  Ibs.  per  square  foot  of  heating  surface  per  hour.  The  author's  for- 
mula, in  which  the  efficiency  is  shown  to  be  a  function  of  six  different 
variables,  is  given  in  the  chapter  on  Efficiency  of  Heating  Surface. 
(Formulas  13,  14,  and  15,  page  219.) 

Range  of  Results  Obtained  from  Anthracite  Coal. — Selecting  the 


290 


STEAM-BOILER  ECONOMY. 


highest  resultc  obtained  at  different  rates  of  driving  with  anthracite 
coal  in  the  Centennial  tests  in  1876,  and  the  highest  results  with 
anthracite  reported  by  Mr.  Barrus  in  his  book  on  Boiler  Tests,  the 
two  curves  in  the  diagram,  Fig.  107,  have  been  plotted,  showing  the 
maximum  results  which  may  be  expected  with  anthracite  coal,  the  first 


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Lbs. Water  Evaporated  per  sq.ft.  of  Heating  Surface  per  Hour. 
FIG.  107.— RESULTS  OF  TESTS  WITH  ANTHRACITE  COAL. 

under  exceptional  conditions,  such  as  obtained  in  the  Centennial  tests,, 
and  the  second  under  the  best  conditions  of  ordinary  practice  (Trans. 
Am.  Soc.  M.  E.,.vol.  xviii.  p.  354).  From  these  curves  the  following 
figures  are  obtained : 

Lbs.  water  evaporated  from  and  at  212°  per  sq.  ft.  heating  surface  per  hour  : 

2         2.5        3          3.5          4        4.5         5        6  78 

Lbs.  water  evaporated  from  and  at  212°  per  Ib.  combustible  : 

Centennial 12.       12.1       12.1       12.        11.8511.7      11.4510.8      9.8    8.5 

Barrus 11.6511.65    11.55     11.4      11.2     10.95    10.6      9.9      9.2    85 

Avg.  Cent'l 12.0    11.6      11.2      10.8      10.4    10.0        9.6      8.8      8.0    7.2 

The  figures  in  the  last  line  are  taken  from  a  straight  line  drawn  as 
nearly  as  possible  through  the  average  of  the  plotting  of  all  the  Cen- 
tennial tests.  The  poorest  results  are  far  below  these  figures.  It  is 
evident  that  no  formula  can  be  constructed  that  will  express  the  rela- 


BOILER  HORSE-POWER. 


291 


tion  of  economy  to  rate  of  driving  as  well  as  do  the  three  lines  of 
figures  given  above. 

The  following  table  gives  the  principal  results  obtained  in  the 
economy  trials  at  the  Centennial  Exhibition,  together  with  the  capacity 
and  economy  figures  of  the  capacity  trials  for  comparison :  * 


Economy  Tests. 

Capacity  Tests. 

£«• 

| 

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5s- 

«B 

«3 

*  I. 

ttj 

£ 

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gaJ 

§JI 

3 

$ 

CM 

cS  ~ 

Name 

a1  . 

flM 

S*Jj 

a 

.: 

& 

pK 

of 
Boiler. 

Water-heal 
to  Grate-s 

urned  per 
e  per  Hour 

+9 

a 

<M      . 

d^ 

II, 

11^ 

g.»& 

rature  in  t 

a 

leating  of  i 

power. 

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8 

PH 

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^ 

EH 

a 

do 

ft 

K 

£N' 

Ibs. 

p.ct. 

Ibs. 

Ibs. 

deg. 

p.ct. 

deg. 

H.P. 

H.P.  ,    Ibs. 

Ibs. 

Root 

34.6 

9  1 

10  4 

2  59 

12  094 

393 

41  4 

119  8 

148  ft  10  441 

3  21 

64  3 

12  0 

10  4 

1  93 

11  988 

415 

32  6 

57  8 

68  4  1  1  064 

?  °9 

Lowe  

30.6 

6.8 

11.3 

2.15 

11.923 

333 

9.4 

47.0 

69.3  11.163 

3.17 

Smith 

45.  ft 

12.1 

11  1 

2  79 

11.006 

411 

1  3 

99  8 

125  0  11  925 

3  74 

Babcock  &  Wilcox. 

37.7 

10.0 

11.0 

2.79 

11.822 

296 

2.7 

135.6 

186.6110.330 

3.84 

Galloway 

23.7 

9.6 

11.1 

4  18 

11  583 

303 

1  4 

103  3 

133  8  ill  216 

5  41 

do    semi-bit,  coal. 

23.7 

7.9 

8.8 

3.68 

12.125 

325 

0.8 

90.9 

125.1  111.609 

5.06 

Andrews  

15.6 

8.0 

10.3 

2.67 

11.039 

420 

71.7 

42.6 

58.7 

9.745 

4.00 

Harrison     

27.3 

12.4 

8.5 

3.16 

10.9'iC 

517 

0.9 

£2  4 

108  4 

9  889 

4  15 

Wiegand  

30.7 

12.3 

9.5 

3.80 

10.834 

524 

20.5 

147.5 

162.8 

9.145 

4.19 

Anderson  

17.5 

9.7 

9.3 

3.03 

10.61S 

417 

15.7 

98.  C 

132.8 

9.568 

4.11 

Kelly  

20.9 

10.8 

9.0 

4.40 

10.312 



5.6 

81.0 

99.9 

8.397 

5.43 

Exeter     .. 

33.5 

9  3 

11.4 

1  59 

10  041 

430 

4.2 

72  1 

108  0 

9  974 

2  38 

Pierce  

14.0 

8.0 

11.0 

5.11 

10.021 

374 

5.2 

51.7 

67.8 

9.865 

6.70 

Rogers  &  Black.... 

19.0 

8.6 

9.9 

3.94 

9.613 

572 

2.1 



45.7 

67.2 

9.429 

5.80 

Averages 

3.19 

11.123 

85.0 

110.8 

10.251 

4.23 

The  comparison  of  the  economy  and  capacity  trials  shows  that  an 
average  increase  in  capacity  of  30  per  cent  was  attended  by  a  decrease 
in  economy  of  8  per  cent,  but  the  relation  of  economy  to  rate  of 
driving  varied  greatly  in  the  different  boilers.  In  the  Kelly  boiler  an 
increase  in  capacity  of  22  per  cent  was  attended  by  a  decrease  in 
economy  of  over  18  per  cent,  while  the  Smith  boiler,  with  an  increase 
of  25  per  cent  in  capacity  showed  a  slight  increase  in  economy.  The 
results  are  plotted  on  the  diagram,  Fig.  107. 

For  semi-bituminous  and  bituminous  coals  the  relation  of  economy 
to  the  rate  of  driving  follows  the  same  general  law  that  it  does  with 
^anthracite,  i.e.,  that  beyond  a  rate  of  evaporation  of  3  or  4  Ibs.  per 
sq.  ft.  of  heating  surface  per  hour  there  is  a  decrease  of  economy,  but 
the  figures  obtained  in  different  tests  will  show  a  wider  range  between 
maximum  and  average  results  on  account  of  the  fact  that  it  is  more 
difficult  with  bituminous  than  with  anthracite  coal  to  secure  complete 
combustion  in  the  furnace. 


*  Reports  and  Awards  Group  XX,  International  Exhibition,  Phila.,  1876;  also, 
Clark  on  the  Steam-engine,  vol.  i.  p.  253. 


CHAPTER  XII. 

"POINTS"   OF   A  GOOD   BOILER. 

THE  boilers  which  have  been  described  and  illustrated  in  chapter  X 
include  all  the  types  which  are  extensively  used  in  land  practice  in 
the  United  States.  They  offer  enough  variety  to  satisfy  the  ideas  or 
prejudices  of  all  classes  of  purchasers.  Boilers  of  each  of  these  types, 
more  or  less  modified,  with  one  or  two  exceptions,  are  made  by 
more  than  one  builder,  the  fundamental  patents  on  all  of  them 
having  expired,  and  competition  between  rival  builders  is  so  intense 
that  any  kind  of  boiler  may  now  be  purchased  at  a  slight  advance 
over  its  cost  to  the  builder.  The  factory  cost  has  also  been  greatly 
reduced  by  the  introduction  of  improved  machinery  and  by  the 
reduced  prices  of  raw  material.  It  would  be  out  of  place  here  to 
recommend  any  one  type  of  boiler  as  superior  to  any  other,  but  some 
ideas  may  be  given  in  regard  to  the  good  and  bad  "points  "  of  boilers 
in  general,  which  may  be  of  assistance  to  an  intending  purchaser  or 
:an  engineer  who  is  confused  by  the  conflicting  statements  of  rival 
builders  or  salesmen. 

Selecting  a  New  Type  of  Boiler. — The  problem  of  selecting  a  new 
form  of  boiler  to  replace  one  of  an  old  type  is,  to  the  average  steam- 
nser,  one  of  considerable  difficulty  on  account  of  the  vast  variety  of 
styles  that  are  now  offered  in  the  market,  and  the  conflicting  state- 
ments of  rival  builders.  The  evolution  of  the  steam-boiler  has  now 
reached  a  period  of  extreme  confusion,  in  which  diversity  of  form  is 
the  leading  feature.  In  other  lines  of  engineering  we  have  reached 
standard  types  which  are  accepted  the  world  over  as  being  the  best 
available.  Thus  there  has  been  no  radical  change  in  the  type  of  loco- 
motive for  fifty  years.  The  Scotch  boiler  is  in  almost  universal  use 
for  marine  purposes.  For  transatlantic  steamships  and  for  high-duty 
pumping-engines,  scarcely  any  other  kind  of  an  engine  than  a  vertical 
triple-expansion  engine  would  be  thought  of.  The  Corliss  engine  has 

292 


"POINTS"  OF  A   GOOD  BOILER.  293 

"been  accepted  as  the  standard  high-class  engine  for  land  purposes  for 
forty  years.  But  in  land  boilers  we  not  only  have  the  variety  of  styles 
shown  in  the  table  already  given  of  percentages  of  different  styles 
used  in  several  countries  of  Europe,  but  in  the  United  States  there  is 
a  continual  procession  of  new  forms  through  the  Patent  Office,  of 
which  enough  find  builders  and  advertisers  to  continually  add  to  the 
existing  confusion. 

The  claims  made  for  these  new  forms  of  boilers  are  generally  in 
inverse  ratio  to  their  merits.  The  following  are  extracts  from  adver- 
tisements in  a  single  issue  of  one  trade  journal  in  February,  1897: 

No.  1.— We  guarantee  you  a  saving  of  from  10  to  25  per  cent  with 
equal  horse-power,  or  an  increase  of  horse-power  of  from  10  to  25  per 
cent  with  the  same  fuel  if  you  use  the steam-generator. 

No.  2. — The  circulation  positively  prevents  scale. 

No.  3. — The  best  boiler  ever  built,  combining  many  points  of  merit 
not  contained  in  any  other  boiler.  Will  evaporate  the  largest  amount 
of  water  per  pound  of  coal. 

No.  4. — Is  an  efficiency  of  30  per  cent  above  all  others  of  interest 
to  you  ?  Send  for  particulars. 

No.  5.— An  evaporation  of  14.66  Ibs.  of  water  from  and  at  212° 
per  pound  of  combustible. 

It  is  worthy  of  note  that  none  of  the  large  boiler  companies,  who 
have  reputations  established  for  many  years,  advertise  in  this  manner, 
and  of  the  boilers  which  are  advertised  in  the  above  extracts,  not  one 
has  any  exceptional  merit  which  would  warrant  its  being  selected  in 
preference  to  the  best  of  the  older  and  better-known  boilers.  It  is 
simply  impossible  that  any  one  of  these  new  boilers  can,  in  an  accurate 
test,  evaporate  14.66  Ibs.  of  water,  from  and  at  212°,  per  Ib.  of  com- 
bustible (if  coal  is  used  as  fuel,  it  might  do  this  and  more  with  petro- 
leum), or  that  any  one  of  them  can  show  10  per  cent  better  economy 
than  a  well-proportioned  boiler  of  older  form,  or  that  any  kind  of  cir- 
culation can  keep  a  boiler  free  from  scale  or  from  deposits  of  solid 
matter  if  the  water  contains  scale-forming  material. 

The  moral  is  this:  Do  not  place  any  reliance  in  the  advertisement 
of  a  boiler  which  claims  that  it  is  superior  to  all  other  boilers  in  fuel- 
economy  or  in  prevention  of  scale.  The  largest  and  most  successful 
boiler  concerns,  who  make  as  good  boilers  as  have  ever  been  made,  or 
are  likely  to  be  made  for  some  years  to  come,  do  not  advertise  in  this 
way. 

Economy  of  Fuel. — Let  it  be  assumed  that  all  the  boilers  offered 


294  STEAM-BOILER  ECONOMY. 

for  choice  are  built  by  makers  of  good  repute,  that  the  quality  of  ma- 
terial and  workmanship  is  beyond  question,  and  that  the  dimensions 
and  arrangement  of  all  the  parts  are  so  chosen  that  they  are  all  equally 
safe  to  resist  a  bursting  pressure.  These  essentials  of  good  boiler  con- 
struction may  be  secured  with  any  of  the  types  described,  by  having 
the  specifications  properly  drawn  and  by  rigid  inspection  of  the  mate- 
rial and  workmanship.  The  economy  of  fuel  which  may  be  obtained 
with  any  boiler  does  not  depend  upon  the  type  of  boiler,  but  upon  its 
proportions,  such  as  the  amount  of  heating  and  grate-surface  furnished 
for  a  given  horse-power,  upon  the  kind  of  furnace  used,  and  upon  the 
arrangement  of  the  gas-passages  so  as  to  cause  the  gas  to  give  up  as 
large  a  percentage  of  its  heat  as  possible  to  the  heating  surface. 
These  are  matters  of  engineering  design  with  any  type  of  boiler,  and 
any  boiler  may  have  them  so  arranged  as  to  cause  it  to  give  as  high 
an  economy  of  fuel  as  is  possible  with  any  other  boiler.  Questions 
that  arise  under  this  head  in  regard  to  any  boiler  are:  1.  Is  the  grate- 
surface  sufficient  for  burning  the  maximum  quantity  of  coal  expected 
to  be  used  at  any  time,  taking  into  consideration  the  available  draft, 
the  quality  of  the  coal,  its  percentage  of  ash,  whether  or  not  the  ash 
tends  to  run  into  clinker,  and  the  facilities,  such  as  shaking  grates, 
for  getting  rid  of  the  ash  or  clinker  ?  2.  Is  the  furnace  of  a  kind 
adapted  to  burn  the  particular  kind  of  coal  used  ?  3.  Is  the  heating 
surface  of  extent  sufficient  to  absorb  so  much  of  the  heat  generated 
that  the  gases  escaping  into  the  chimney  shall  be  reasonably  low  in 
temperature,  say  not  over  400°  F.  with  anthracite  and  500°  F.  with 
bituminous  coal  ?  4.  Are  the  gas-passages  so  designed  and  arranged 
as  to  compel  the  gas  to  traverse  at  a  uniform  rate  the  whole  of  the 
heating  surface,  not  being  so  large  at  any  point  as  to  allow  the  gas  to 
find  a  path  of  least  resistance  or  be  short-circuited,  or,  on  the  other 
hand,  so  contracted  at  any  point  as  to  cause  an  obstruction  to  the  draft  ? 
These  questions  being  settled  in  favor  of  any  given  boiler,  and 
they  may  be  answered  favorably  for  boilers  of  any  of  the  modern 
types  already  described,  provided  the  furnaces  and  boilers  are  prop- 
.  r.erly  designed/the  relative  merits  of  the  different  types  may  now  be 
considered  with  reference  to  their  danger  of  explosion;  their  probable 
durability;  the  character  and  extent  of  repairs  that  may  be  needed 
from  time  to  time,  and  the  difficulty,  delay,  and  expense  that  these 
may  entail;  the  accessibility  of  every  part  of  the  boiler  to  inspection, 
internal  and  external;  the  facility  for  removal  of  mud  and  scale  from 
every  portion  of  the  inner  surface,  and  of  dust  and  soot  from  the  ex- 


"POINTS"   OF  A   GOOD  BOILER.  295 

/  terior;  the  water-  and  steam-capacity;   the  steadiness  of  water-level; 

*  and  the  arrangements  for  securing  dry  steam.) 

Each  one  of  the  points  above  referred  to  should  be  considered 
carefully  by  the  intending 'purchaser  of  any  type  of  boiler  with  which 
he  is  not  familiar  by  experience.  The  several  points  may  be  consid- 
ered more  in  detail. 

Danger  of  Explosion. — All  boilers  may  be  exploded  by  over-press- 
ure, such  as  might  be  caused  by  the  combination  of  an  inattentive 
fireman  and  an  inoperative  safety-valve,  or  by  corrosion  weakening 
the  boiler  to  such  an  extent  as  to  make  it  unable  to  resist  the  regular 
working  pressure;  but  some  boilers  are  much  more  liable  to  explosion 
than  others.  In  considering  the  probability  of  explosion  of  any  boiler 
of  recent  design,  it  is  well  to  study  it  to  discover  whether  or  not  it  has 
any  of  the  features  which  are  known  to  be  dangerous  in  the  plain, 
cylinder,  the  horizontal  tubular,  the  vertical  tubular  and  the  locomo- 
tive boilers.  fThe  plain  cylinder  boiler  is  liable  to  explosion  from 
strains  induced  by  its  method  of  suspension,  and  by  changes  of  tem- 
perature. Alternate  expansion  and  contraction  may  produce  a  line  of 
weakness  in  one  of  the  rings,  which  may  finally  cause  an  explosion. 
A  boiler  should  be  so  suspended  that  all  its  parts  are  free  to  change 
their  position  under  changes  of  temperature  without  straining  any  part. 
The  circulation  of  water  in  the  boiler  should  be  sufficient  to  keep  all 
parts  at  nearly  the  same  temperature.  Cold  feed-water  should  not  bo 
allowed  to  come  in  contact  with  the  shell,  as  this  will  cause  contrac- 
tion and  strain.]  The  horizontal  tubular  boiler,  and  all  externally 
fired  shell  boilers,  are  liable  to  explosion  from  overheating  of  the 
shell,  due  to  accumulation  of  mud,  scale  or  grease  on  the  portion  of 
the  shell  lying  directly  over  the  fire;  to  a  double  thickness  of  iron,  as  at 
a  lap-joint,  together  with  some  scale,  over  the  fire;  or  to  low  water 
uncovering  and  exposing  an  unwetted  part  of  the  shell  directly  to 
the  hot  gases.  /Vertical  tubular  boilers  are  liable  to  explosion  from 
deposits  of  mud,  scale  or  grease  upon  the  lower  tube-sheet,  and 
from  low  water  allowing  the  upper  part  of  the  tubes  to  get  hot  and 
cease  to  act  as  stays  to  the  upper  tube-sheet. |  Locomotive  boilers  may 
explode  from  deposits  on  the  crown-sheet,  irom  low  water  exposing 
the  dry  crown-sheet  to  the  hot  gases,  and  from  corrosion  of  the  stay- 
bolts.  Double-cylinder  boilers,  such  as  the  French  elephant  boiler, 
and  the  boilers  used  at  some  American  blast-furnaces,  have  exploded 
on  account  of  the  formation  of  a  "  steam-pocket"  on  the  upper  por- 
tion of  the  lower  cylinder,  the  steam  being  prevented  from  escaping  by 


296  STEAM-BOILER  ECONOMY. 

the  lap-joint  of  one  of  the  rings,  thus  making  a  layer  of  steam  about 
i  inch  thick  against  the  shell  which  was  directly  exposed  to  the  hot 


The  above  mentioned  are  only  a  few  of  the  causes  of  explosions, 
but  they  are  the  principal  ones  that  are  due  to  features  of  design. 
These  features  should  be  looked  for  in  any  new  style  of  boiler,  and  if 
they  are  found  they  should  be  considered  elements  of  danger.  Such 
questions  as  the  following  may  be  asked  :  Is  the  method  of  suspen- 
sion of  the  boiler  sucn  as  to  allow  its  parts  to  be  free  to  move  under 
changes  of  temperature  ?  Is  the  circulation  such  as  to  keep  all  parts 
at  practically  the  same  temperature  ?  Is  there  a  shell  with  riveted 
seams  exposed  to  the  fire  ?  Is  there  a  shell  exposed  to  the  fire  which 
may  at  any  time  be  uncovered  by  water  or  be  covered  with  scale  ?  Is 
there  a  crown-sheet  on  which  scale  may  lodge  ?  Are  there  sufficient 
facilities  for  the  removal  of  scale?  Are  there  vertical  or  inclined 
tubes  acting  as  stays  to  an  upper  sheet,  the  upper  part  of  which  tubes 
may  become  overheated  in  case  of  low  water  ?  Are  there  any  stayed 
sheets,  the  stays  of  which  are  liable  to  become  corroded  ?  Is  there  any 
chance  for  a  steam-pocket  to  be  formed  on  a  sheet  which  is  exposed 
to  the  fire  ? 

In  addition  to  the  above-mentioned  features  of  design,  which  are 
elements  of  danger,  all  boilers,  as  already  stated,  are  liable  to  explosion 
due  to  corrosion.  Internal  corrosion  is  usually  due  to  acid  feed-water, 
or  to  very  pure  feed-water  containing  dissolved  air,  and  all  boilers 
are  equally  liable  to  it.  External  corrosion,  however,  is  more  liable 
to  take  place  in  some  designs  of  boilers  than  in  others,  and  in  some 
locations  rather  than  in  others.  If  any  portion  of  a  boiler  is  in  a 
cold  and  damp  place,  it  is  liable  to  rust  out.  For  this  reason  the  mud- 
drums  of  many  modern  forms  of  boilers  are  made  of  cast  iron,  which 
resists  rusting  better  than  either  wrought  iron  or  steel.  If  any  part 
of  a  boiler,  other  than  a  part  made  of  cast  iron,  is  liable  to  be  exposed 
to  a  cold  and  damp  atmosphere,  or  covered  with  damp  soot  or  ashes, 
or  exposed  to  drip  from  rain  or  from  leaky  pipes,  and  especially  if  such 
part  is  hidden  by  brickwork  or  otherwise  so  that  it  cannot  be  inspect- 
ed, that  part  is  an  element  of  danger. 

Durability. — The  question  of  durability  is  partly  covered  by  that 
of  danger  of  explosion,  which  has  already  been  discussed,  but  it  also  is 
related  to  the  question  of  incrustation  and  scale.  The  plates  and 
tubes  of  a  boiler  may  be  destroyed  by  internal  or  external  corrosion, 
but  they  may  also  be  burned  out.  It  may  be  regarded  as  impossible 


"POINTS"   OF  A   GOOD  BOILER.  29T 

to  burn  a  plate  or  tube  of  iron  or  steel,  no  matter  how  high  the  tem- 
perature of  the  flame,  provided  one  side  of  the  metal  is  covered  with 
water.  If  a  steam-pocket  is  formed,  so  that  the  water  does  not  touch 
the  metal,  or  if  there  is  a  layer  of  grease  or  hard  scale,  then  the  plate 
or  tube  may  be  burned.  In  a  water-tube  which  is  horizontal,  or 
nearly  so,  and  in  which  the  circulation  of  water  is  defective,  it  is  pos- 
sible to  form  a  mass  of  steam  which  will  drive  the  water  away  from 
the  metal,  and  thus  allow  the  tube  to  burn  out.  In  considering  the 
probable  durability  of  a  boiler,  we  may  ask  the  same  questions  as  those 
that  have  been  asked  concerning  danger  of  explosion.  There  are, 
however,  many  chances  of  burning  out  a  minor  part  of  a  boiler  with- 
out serious  danger,  to  one  chance  of  a  disastrous  explosion.  Thus 
the  tubes  of  a  water-tube  boiler,  if  allowed  to  become  thickly  cov- 
ered with  scale,  might  be  burned  out  without  causing  any  further  de- 
struction than  the  rupture  of  a  single  tube.  A  new  type  of  boiler 
should  be  questioned  in  regard  to  the  likelihood  of  frequent  small 
repairs  being  necessary,  and  as  well  in  regard  to  its  liability  to  com- 
plete destruction.  We  may  ask:  Is  the  circulation  through  all  parts/ 
of  the  boiler  such  that  the  water  cannot  be  driven  out  of  any  tube  or/ 
from  any  portion  of  a  plate,  so  as  to  form  a  steam-pocket  exposed  tew 
high  temperature  ?  Are  there  proper  facilities  for  removing  the  scale/- 
from  every  portion  of  the  plates  and  tubes  ? 

Repairs. — The  questions  of  durability  and  of  repairs  are,  in  some 
respects,  related  to  each  other.  The  more  infrequent  and  the  less 
extensive  the  repairs,  the  greater  the  durability.  The  tubes  of  a  boiler, 
where  corroded  or  burnt  out,  may  be  replaced,  and  made  as  good  as 
new.  The  shell,  when  it  springs  a  leak,  may  be  patched,  and  is  then 
likely  to  be  far  from  as  good  as  new.  When  the  shell  corrodes  badly 
it  must  be  replaced,  and  to  replace  the  shell  is  the  same  as  getting  a, 
new  boiler.  Herein  is  the  advantage  of  the  sectional  water-tube  boil- 
ers. The  sections,  or  parts  of  a  section,  may  be  renewed  easily,  and 
made  good  as  new,  while  the  shell,  being  far  removed  from  the  fire  and 
easily  kept  dry  externally,  is  not  liable  either  to  burning  out  or  exter- 
nal corrosion.  In  considering  the  merits  of  a  new  style  of  boiler, 
with  reference  to  repairs,  we  may  ask  what  parts  of  the  boiler  are 
most  likely  to  give  out  and  need  to  be  repaired  or  replaced  ?  Are 
these  repairs  easily  effected;  how  long  will  they  require;  and  after 
they  are  made  is  the  boiler  as  good  as  now?  If  a  new  style  of  boiler 
made  up  of  special  parts  not  procurable  except  from  its  builder,  tha 


298  STEAM-BOILER  ECONOMY. 

question  may  be  asked  :  How  long  is  the  builder  likely  to  remain  in 
business  and  be  able  to  furnish  these  special  parts  ? 

Facility  for  Removal  of  Scale  and  for  Inspection.— These  questions 
have  already  been  discussed  to  some  extent  under  the  head  of  dura- 
bility. Some  water-tube  boilers,  now  dead  and  gone,  were  some  years 
ago  put  on  the  market,  which  had  no  facilities  for  the  removal  of 
scale.  It  was  claimed  by  their  promoters  that  they  did  not  need  any, 
because  their  circulation  was  so  rapid.  Every  few  years  boilers  of 
these  types  are  re-invented,  and  the  same  claim  is  made  for  them,  that 
their  rapid  circulation  prevents  the  formation  of  scale.  The  fact  is 
that  if  there  is  scale-forming  material  in  the  water  it  will  be  deposited 
when  the  water  is  evaporated,  and  no  amount  or  kind  of  circulation 
will  keep  it  from  accumulating  on  every  part  of  the  boiler  and  in  every 
kind  of  tubes,  vertical,  horizontal,  and  inclined.  The  nearly  vertical 
circulating  tubes  of  a  water-tube  boiler,  in  which  the  circulation  is 
nine  times  as  fast  as  the  average  circulation  in  the  inclined  tubes, 
sometimes  have  been  found  nearly  full  of  scale  ;  that  is,  a  4-inch  tube 
had  an  opening  in  it  of  less  than  1  inch  diameter.  This  was  due  to 
carelessness  in  blowing  off  the  boiler,  or  exceptionally  bad  feed-water, 
or  both.  If  circulation  would  prevent  scaling  at  all,  it  would  pre- 
vent it  here. 

Water-  and  Steam-capacity. — It  is  claimed  for  some  forms  of  boil- 
ers that  they  are  better  than  others  because  they  have  a  larger  water- 
•or  steam-capacity.  Great  water-capacity  is  useful  where  the  demands 
for  steam  are  extremely  fluctuating,  as  in  a  rolling-mill  or  a  sugar- 
refinery,  where  it  is  desirable  to  store  up  heat  in  the  water  in  the  boil- 
ers during  the  periods  of  the  least  demand,  to  be  given  out  during 
periods  of  greatest  demand.  Large  water-capacity  is  objectionable  in 
boilers  for  factories,  usually,  especially  if  they  do  not  run  at  night, 
and  the  boilers  are  cooled  down,  because  there  is  a  large  quantity  of 
water  to  be  heated  before  starting  each  morning.  If  "rapid  steam- 
ing" or  the  ability  to  get  up  steam  quickly  from  cold  water,  or  to 
raise  the  pressure  quickly,  is  desired,  large  water-capacity  is  a  detri- 
ment. The  advantage  of  large  steam-capacity  is  usually  overrated.  It 
is  useful  to  enable  the  steam  to  be  drained  from  water  before  it 
•escapes  into  the  steam-pipe,  but  the  same  result  can  be  effected  by 
means  of  a  dry  pipe,  as  in  locomotive  and  marine  practice,  in  which 
the  steam-space  in  the  boiler  is  very  small  in  proportion  to  the  horse- 
power. Large  steam-space  in  the  boiler  is  of  no  importance  for  stor- 
ing energy  or  equalizing  the  pressure  during  the  stroke  of  an  engine. 


"POINTS"   OF  A   GOOD  BOILEIt.  299 

The  water  in  the  boiler  is  the  place  to  store  heat,  and  if  the  steam- 
pipe  leading  to  an  engine  is  of  such  small  capacity  that  it  reduces  the 
pressure,  the  remedy  is  a  steam-reservoir  close  to  the  engine  or  a  large 
steam -pipe. 

Steadiness  of  Water-level.— This  requires  either  a  large  area  of 
water-surface  and  volume  of  water,  so  that  the  level  may  be  changed 
slowly  by  fluctuations  in  the  demand  for  steam  or  in  the  delivery  of 
the  feed-pump,  or  else  constant,  and  preferably  automatic,  regula- 
tion of  the  feed-water  supply  to  suit  the  steam  demand.  A  rapidly 
lowering  water-level  is  apt  to  expose  dry  sheets  or  tubes  to  the 
action  of  the  hot  gases,  and  thus  be  a  source  of  danger.  A  rapidly 
rising  level  may,  before  it  is  seen  by  the  fireman,  cause  water  to  be 
carried  over  into  the  steam-pipe,  and  endanger  the  engine. 

Large  area  of  water-surface  alone  is  not  always  sufficient  to  insure 
steadiness  of  water-level.  Sudden  fluctuations  in  the  activity  of  the 
fire,  such  as  take  place  when  the  gases  from  freshly-fired  soft  coal 
burst  into  flame,  are  apt  to  cause  a  sudden  rise  in  the  water-level. 
For  this  reason,  boilers  with  horizontal  water-  and  steam-drums, 
whether  fire- tube  or  water-tube  boilers,  should  preferably  have  drums 
not  less  than  30  ins.  diameter,  so  that  the  water-level  may  be  allowed 
to  vary  5  or  6  ins.  from  its  normal  position  without,  on  the  one  hand, 
endangering  the  burning  out  of  the  tubes,  or,  on  the  other,  of  making 
wet  steam. 

Dryness  of  Steam. — Most  of  the  modern  forms*  of  both  fire-tube 
and  water-tube  boilers  give  practically  dry  steam,  that  is,  steam  con- 
taining not  over  1|  %  of  moisture,  when  the  water-level  is  not 
allowed  to  rise  more  than  5  or  6  ins.  above  its  mean  position,  even 
when  driven  as  much  as  100  %  beyond  their  rated  capacity ;  but  boil- 
ers with  vertical  tubes,  with  small  water-level  area,  are  apt,  sometimes, 
to  have  the  water-level  fluctuate  violently,  and  they  require  to  be  pro- 
vided with  superheating  surface  and  dry  pipes,  or  steam  separators,  in 
order  to  insure  dry  steam.  Alkaline  feed -water  is  often  a  cause  of 
"foaming,"  causing  wet  steam. 

Water-circulation. — Positive  and  complete  circulation  of  the  water 
in  a  boiler  is  important  for  two  reasons  :  (1)  To  keep  all  parts  of  the 
boiler  of  a  uniform  temperature,  and  (2)  to  prevent  the  adhesion  of 
steam-bubbles  to  the  surface,  which  may  cause  overheating  of  the 
metal.  It  is  claimed  by  some  manufacturers  that  the  rapid  circula- 
tion of  water  in  their  boilers  tends  to  make  them  more  economical 
than  others.  We  have  as  yet,  however,  to  find  anv  proof  that  increased 


300  STEAM-BOILER  ECONOMY. 

rapidity  of  circulation  of  water  beyond  that  usually  found  in  any 
boiler  will  give  increased  economy.  We  know  that  increased  rale 
of  flow  of  air  over  radiating  surfaces  increases  the  amount  of  heat 
transmitted  through  the  surface,  but  this  is  because  by  the  increased 
circulation  cold  air  is  continually  brought  in  contact  with  the  surface, 
making  an  increased  difference  of  temperature  on  the  two  sides,  which 
causes  increased  transmission.  But  by  increasing  the  rapidity  of  cir- 
culation in  a  steam-boiler  we  cannot  vary  the  difference  of  tempera- 
ture to  any  appreciable  extent,  for  the  water  and  the  steam  in  the 
boiler  are  at  about  the  same  temperature  throughout.  The  ordinary 
or  "  Scotch"  form  of  marine  boiler  shows  an  exception  to  the  general 
rule  of  uniformity  of  temperature  of  water  throughout  the  boiler, 
but  the  temperature  above  the  level  of  the  lower  fire-tubes  is  practi- 
cally uniform. 


CHAPTER  XIII. 
BOILER  TROUBLES  AND  BOILER-USERS'  COMPLAINTS. 

IT  is  the  experience  of  every  large  boiler-making  concern  that  of 
all  the  boilers  it  sells,  a  certain  proportion  are,  shortly  after  erection, 
complained  of  by  the  purchaser  as  being  unsatisfactory.     When  such 
complaints  are  received,  an  expert  in  boiler- testing  and  management 
is  usually  sent  to  make  an  investigation,  and,  if  possible,  to  remedy 
the  trouble.     In  most  cases  he  succeeds,  after  a  great  deal  of  dif- 
ficulty, in  satisfying  the  purchaser,  either  by  improving  the  conditions 
of  the  running  of  the  boiler  or  by  showing  that  the  boiler  is  not  to 
blame   for  the  trouble;  but  sometimes  he  fails,  and  the  matter  is 
finally  adjusted  by  the  boiler  being  taken  out,  by  a  reduction  in  the 
price,  or  by  recourse  to  arbitration,  or  to  a  law-suit.      In  a  law-suit 
the   boiler-maker  usually  wins,  for  the  reason  that  a  boiler-maker, 
having  had  previous  experience  in  such  matters,  is  not  apt  to  go  to 
law  unless  he  has  a  very  strong  case.      The   purchaser,  of   course, 
also  thinks  he  has  a  strong  case,  but  he  is  apt  to  be  not  well  posted  on 
the  law  of  contracts,  and  his  attorney  is  apt  to  be  ignorant  of  the 
amount  of  evidence  which  the  boiler-maker  will  bring  forward  on  the 
trial,  and  therefore  underrates  the  strength  of  the  boiler-maker's  side 
of  the  case.     It  is  the  object  of  this  chapter  to  discuss,  not  the  troubles 
and  complaints  concerning  boilers  in  their  relation  to  possible  law- 
suits, but  those  that  maybe  avoided  or  remedied  by  good  engineering. 
The  complaints  from  boiler-users  concerning  new  boilers  may  be 
divided  into  three  general   classes:   1,  Low  capacity;   2,  Structural 
defects,  such  as  leaks,  burnt  tubes  and  plates,  etc.;  3,  Poor  economy. 
The  last  is  not  often  a  cause  of  complaint,  because  the  great  majority 
of  boiler-users  make  no  tests  to  determine  economy,  and  therefore  if 
their  boilers  should  be  deficient  in  economy,  they  are  ignorant  of  it. 
But  if  a  boiler  does  not  give  the  amount  of  steam  that  is  needed  from 
it,  or  if  it  leaks,  the  trouble  is  apparent  at  once  and  complaint  is  made 
immediately. 

301 


302  STEAM-BOILER  ECONOMY. 

The  most  common "  causes  of   complaints  and  troubles  are  the 
following: 

1.  Poor  draft. 

2.  Insufficient  grate  surface. 

3.  Poor  coal. 

4.  Furnace  not  adapted  to  kind  of  coal. 

5.  Bad  setting  of  boiler. 

6.  Leaks  of  air  through  brickwork. 

7.  Improper  firing. 

8.  Insufficient  heating  surface  (boiler  too  small). 

9.  Bad  water. 

We  will  now  discuss  these  causes  of  trouble,  and  their  remedies,  in 
the  order  named. 

Poor  Draft. — This  is  a  relative  term;  what  is  poor  draft  for  one 
set  of  conditions  is  ample  draft  for  another.  The  proper  force  of 
draft  for  a  given  case,  measured  at  a  point  between  the  damper  in  the 
flue  and  the  boiler  itself,  may  be  as  low  as  £  inch  of  water-column, 
and  in  another  case  over  1  inch  may  be  required,  depending  on  the 
type  of  boiler,  on  the  area  and  the  course  of  the  draft-passage  through 
the  boiler,  on  the  area  of  grate  surface,  on  the  style  of  grate-bars, 
and  on  the  kind  of  coal.  The  immediate  effect  of  poor  draft  is  insuf- 
ficient coal-burning  capacity.  The  first  test  to  be  applied  to  discover 
whether  or  not  the  draft  is  insufficient  is  to  weigh  the  coal  burned 
in  each  hour  during  the  period  between  two  cleanings  of  the  grates, 
and  to  compare  the  amounts  burned  each  hour  with  the  amount 
which  a  calculation  shows  should  be  burned  to  evaporate  the  desired 
amount  of  water.  Thus,  suppose  that  it  is  expected  that  the  toiler 
should  evaporate  3500  Ibs.  of  water  per  hour,  and  the  temperature  of 
feed -water,  the  steam-pressure,  and  the  quality  of  coal  are  such  that 
7  Ibs.  of  water  should  be  evaporated  per  pound  of  coal,  then  the  coal- 
burning  capacity  should  be  not  less  than  500  Ibs.  during  each  hour 
between  cleanings.  If  200  Ibs.  is  used  in  the  first  part  of  the  test  to 
build  up  the  fire,  and  an  equal  amount  is  burned  down  at  the  close  of 
the  test,  in  order  to  have  a  thin  bed  of  coal  for  cleaning,  then  a  five- 
hours' record  of  coal  fed  between  cleanings  should  show  approximately 
700,  500,  500,  500..  and  300  Ibs.  If  the  record  gave  600,  400,  400,  400, 
and  200  Ibs.  it  would  indicate  insufficient  draft  for  the  kind  of  grate 
'and  the  kind  of  coal.  If,  however,  it  should  show  700,  £00,  400,  300, 
200  Ibs.,  it  would  indicate  that  the  draft  itself  was  ample,  but  that  the 
grates  were  being  gradually  choked  by  ashes  and  clinkers. 


BOILER   TROUBLES  AND  BOILER-USERS'    COMPLAINTS.     303 

In  the  second  case,  in  which  the  coal  is  burned  steadily  at  the  rate 
of  400  Ibs.  of  coal  per  hour,  when  500  Ibs.  is  required,  the  remedy  in- 
dicated is  an  increase  of  the  draft.  It  will  often  happen  that  such 
remedy  can  easily  be  given  by  a  slight  change  in  the  flue-connection 
between  the  boiler  and  chimney.  Eight-angled  bends  in  this  flue- 
connection  are  exceedingly  common,  and  they  frequently  cut  down 
the  force  of  draft  at  the  boiler  to  one-half  of  that  in  the  chimney. 
Whenever  possible  they  should  be  changed  to  long  easy  curves.  When 
two  or  more  adjoining  boilers  deliver  their  gases  into  one  horizontal 
flue,  the  area  of  this  flue  should  increase  as  it  travels  from  the  most 
distant  boiler  to  the  chimney,  the  connection  from  each  boiler  to  the 
flue  should  be  a  curved  one,  and  the  flue  itself  should  enter  the  chim- 
ney with  an  ascending  curve.  Before  making  the  changes  here  sug- 
gested, the  existing  draft  in  the  chimney,  at  various  points  in  the 
flue,  and  at  each  boiler,  should  be  tested  by  a  U-tube  draft-gauge.  If 
there  are  no  defects  in  the  flue-connection,  the  next  remedy  to  be  ap- 
plied is  an  increase  in  the  height  of  the  chimney.  If  this  is  not  feasi- 
ble, and  a  reference  to  a  table  of  proportions  of  chimneys  shows  that 
the  chimney  has  not  sufficient  area  for  the  amount  of  coal  to  be 
burned,  then  a  new  chimney  with  larger  area  is  required.  In  case  it 
appears  that  the  chimney  is  of  sufficient  area  and  its  height  cannot  be 
increased,  a  remedy  may  be  found  in  enlarging  the  area  of  grate- 
surface  or  in  using  a  different  kind  of  coal. 

If  the  test  of  the  coal-burning  capacity  shows  a  decreasing  rate  of 
burning,  such  as  700,  500,400,  300,  and  200  Ibs.  per  hour,  indicating  a, 
gradual  choking  of  the  grate  by  clinker,  the  most  obvious  remedy  ia 
the  use  of  a  shaking-grate,  by  which  the  accumulation  of  ashes  and 
clinker  may  be  prevented.  Such  a  grate  will  sometimes  increase  the 
capacity  of  a  boiler  as  much  as  30  per  cent,  although  its  use  may 
entail  a  loss  of  economy  of  2  or  3  per  cent  due  to  the  coal  shaken  into 
the  ash-pit  with  the  ashes.  A  change  of  coal  from  a  clinkering  to  a 
non-clinkering  variety  will  sometimes  prove  a  sufficient  remedy. 

With  a  clinkering  coal,  increase  of  draft  is  sometimes  of  no  benefit 
in  increasing  the  capacity  of  a  boiler,  but  rather  the  reverse;  for  when 
the  fire  is  freshly  cleaned,  a  strong  draft  with  such  coal  causes  at  first 
a  rapid  combustion,  resulting  in  high  temperature  and  a  fusing  of  the 
clinker,  which  soon  obstructs  the  passage  of  air  through  the  grates, 
checking  the  combustion.  Enlargement  of  the  grate  surface  and  a 
slower  rate  of  combustion  per  square  foot  of  grate  are  then  the  proper 
remedies,  and  if  these  are  impracticable,  then  shaking-grates  should 


304  STEAM-BOILER  ECONOMY. 

l.e  used.  The  tendency  to  form  clinker  may  sometimes  be  lessened 
by  blowing  a  little  steam  under  the  grate-bars,  or  by  letting  a  little 
"water  run  into  the  ash-pit.  The  evaporation  of  the  water  helps  to  cool 
the  grate-bars. 

Insufficient  Grate  Surface,  and  Poor  Coal. — These  two  causes  of 
trouble  may  be  considered  together  as  they  are  co-related.  Insufficient 
grate  surface  for  one  grade  of  coal  may  be  ample  for  another  grade. 
By  grade  of  coal'tiere  is  meant  its  quality  as  regards  amount  of  ash 
and  kind  of  ash.  If  the  percentage  of  ash  in  the  coal  is  low,  and  it  is 
low  in  iron  and  sulphur,  which  are  the  principal  causes  of  clinker,  a 
relatively  small  grate  surface  and  a  strong  draft  may  be  used,  such, 
for  instance,  as  to  cause  the  burning  of  as  much  as  20  Ibs.  of  anthra- 
cite, 25  or  30  Ibs.  of  semi-bituminous,  and  30  to  40  Ibs.  of  bituminous 
ooal  per  square  foot  of  grate  per  hour;  but  if  the  ash  is  excessive,  or  if 
it  forms  clinker,  then  a  large  grate  is  needed,  so  that  these  rates  of 
combustion  may  be  reduced  30  to  50  per  cent. 

Furnace  Not  Adapted  to  Coal. — Thirty  or  forty  years  ago  it  used  to 
be  the  custom  to  set  boilers  with  the  grate-bars  near  to  the  shell  of 
the  boiler,  12  to  15  ins.  being  a  common  distance,  the  idea  being  that 
there  was  a  loss  of  radiant  heat  if  the  boiler  was  removed  a  greater 
distance  from  the  grate.  The  idea  was  erroneous,  as  may  be  learned 
by  considering  the  question  "If  the  heat  is  lost,  where  does  it  go?" 
A  pound  of  coal,  in  burning  under  a  boiler,  generates  so  many  heat- 
units.  A  small  fraction  of  them  is  lost  through  the  side  walls  of  the 
furnace.  The  heat  radiated  into  the  side  walls  is  radiated  back  again 
to  the  fire,  to  the  heating  surface  of  the  boiler,  to  the  particles  of 
carbon  in  the  flame,  and  to  gaseous  products  of  combustion,  and  it 
finally  all  gets  into  the  boiler  except  that  which  is  carried  out  of  the 
chimney  or  through  the  walls  of  the  setting.  With  dry  anthracite 
coal,  which  burns  practically  without  flame,  almost  any  kind  of  furnace 
is  a  good  one,  but  a  furnace  in  which  the  grate  is  12  or  15  ins.  from 
the  boiler  is  entirely  unsuited  to  the  burning  of  bituminous  coal.  A 
distance  of  from  2  to  3  feet  from  the  grate  to  the  boiler  is  now  com- 
mon practice  for  bituminous  coal.  With  very  smoky  coal,  4  feet  is 
sometimes  used;  and  6  or  8  feet  would  be  better. 

A  furnace  for  a  steam-boiler  is  not  adapted  to  the  coal  whenever 
the  flame  from  the  coal  is  extinguished  by  the  comparatively  cool 
surfaces  of  the  boiler,  and  whenever  it  is  not  possible  by  skilful 
operation  of  the  furnace  to  prevent  smoke  escaping  from  the  chimney.. 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.      305 

.A  smoky  chimney  is  proof  either  of  an  improper  furnace  for  the  kind 
of  coal  or  of  unskilful  firing,  or  both;  usually  of  the  former. 

The  loss  of  economy  and  the  diminution  of  capacity  of  steam- 
boilers  due  to  smoky  chimneys  is  usually  underestimated.  It  is 
•stated  that  it  has  been  found  by  experiment  that  the  amount  of  soot 
actually  present  in  smoke  is  less  than  one  per  cent  of  the  weight  of 
coal  burned.  Numerous  experiments  have  shown  also  that  when 
•"  smoke-consumers"  are  applied  to  a  steam-boiler,  while  the  smoke 
may  be  prevented,  no  gain  in  economy  follows.  This  may  be  quite 
true,  but  the  "smoke-consumers"  referred  to  usually  effect  the 
smoke-prevention  by  means  of  an  excessive  supply  of  air,  which 
involves  waste  of  fuel,  so  that  the  failure  to  show  a  gain  in  economy 
is  due  to  substituting  the  waste  due  to  excessive  air-supply  for  the 
waste  due  to  imperfect  combustion. 

While  it  may  be  true  also  that  the  soot  in  smoke  represents  only 
one  per  cent  of  the  fuel  burned,  this  is  not  the  only  loss  of  fuel  which 
attends  the  smoky  chimney,  for.  the  smoke  not  only  contains  soot,  but 
it  may  also  contain  invisible  hydrocarbon  gases  distilled  from  the  coal, 
arid  carbonic  oxide  produced  in  the  furnace  by  imperfect  combustion 
of  the  carbon. 

Bad  Setting  of  Boiler. — If  the  type  of  setting  is  one  adapted  to  the 
kind  of  coal,  it  may  still  have  errors  of  design  or  of  construction  which 
may  lead  to  the  loss  of  economy  or  of  capacity,  or  of  both.  Examples 
of  such  errors  are  :  (1)  Boiler  set  too  close  to  the  grate.  (2)  Insuffi- 
cient area  through  the  flues,  damper,  or  other  passages  for  the  gas.  (3) 
Excessive  area  of  gas-passages,  so  placed  that  the  gases  can  find  a  path 
of  least  resistance  along  or  across  the  heating  surfaces,  and  thus  be 
"short-circuited."  The  error  of  the  boiler  being  set  too  close  to  the 
grate  has  already  been  discussed.  Insufficient  area  of  gas-passages 
acts  to  choke  the  draft  and  restrict  the  coal-burning  capacity,  just  as 
do  insufficient  chimney  area  or  height,  and  insufficient  grate  area. 
Whether  or  not  the  gas-passages  are  insufficient  in  area  can  usually  be 
determined  by  inspection  and  comparison  of  their  measurements  with 
that  of  the  chimney  and  grate.  A  draft-gauge  should  be  applied  at 
different  points  in  the  gas-passages,  between  the  chimney  and  the 
furnace,  in  order  to  find  whether  there  is  any  serious  choke  in  the  draft. 
This  should  be  done  when  the  fire  is  clean  and  burning  brightly. 

Whether  or  not  the  areas  of  the  gas-passages  are  too  large,  or  such 
as  to  allow  of  short-circuiting  of  the  gases,  is  usually  a  rather  difficult 
matter  to  determine.  The  error  may  be  suspected  to  exist  whenever 


306  STEAM-BOILER  ECONOMY. 

it  is  found  by  an  evaporation-test  that  the  boiler  gives  a  lower  result, 
than  should  be  expected  under  the  conditions,  and  at  the  same  time 
there  is  found  a  high  temperature  of  the  chimney-gases  and  a  low  rate 
of  evaporation  per  square  foot  of  heating  surface.  This  same  set  of 
combined  conditions,  viz.,  low  capacity,  low  economy,  and  high  tem- 
perature of  chimney-gases,  may,  however,  be  the  result  of  imper- 
fect combustion  in  the  furnace  and  burning  of  the  gases  in  the  gas- 
passages  between  the  furnace  and  the  chimney.  If  there  is  no 
evidence  of  imperfect  furnace-conditions  and  of  the  burning  of 
gas  in  the  passages,  then  short-circuiting  of  the  gases  is  probably 
the  cause  of  the  observed  results.  After  making  the  diagnosis  of 
short-circuiting,  another  test  of  the  boiler  should  be  made,  if  suf- 
ficient draft  is  available,  at  a  very  much  higher  rate  of  combustion. 
If  it  is  found  that  this  test  gives  an  increase  of  economy  with  no- 
increase  in  the  temperature  of  the  chimney-gases,  this  would  tend 
to  prove  that  short-circuiting  existed  during  the  first  test.  The  gases 
may  short-circuit  during  the  test  at  a  low  rate  of  driving  and  not  dur- 
ing the  other  test  because  in  the  first  test  the  volume  of  gases  is  rela- 
tively small,  and  in  the  second  it  is  large,  so  that  they  completely  fill 
the  passages.  The  gas-passages  may,  therefore,  be  properly  propor- 
tioned for  a  high  rate  of  driving,  but  may  be  too  large  for  a  low  rate. 

Another  kind  of  test  which  may  be  applied  to  determine  whether 
or  not  there  is  short-circuiting  of  the  gases,  is  the  exploration  of 
various  portions  of  the  gas-passages  by  an  electric  pyrometer,  in  order 
to  discover  if  any  portion  is  not  swept  by  the  current  of  hot  gas.  This 
instrument  is  of  recent  invention,  and  has  not  yet,  to  any  great  extent, 
been  employed  in  boiler-testing,  but  its  use  is  to  be  recommended  in 
future  scientific  investigations  of  steam-boiler  economy  by  boiler  man- 
ufacturers and  others.  It  is  highly  probable  that  many  of  the  very 
low  economic  results  sometimes  obtained  in  boiler-tests,  which  are 
unexplained  by  the  observed  conditions,  are  due  to  this  short-circuit- 
ing, the  existence  of  which  may  be  revealed  by  the  electric  pyrometer. 

When  short-circuiting  of  the  gases  is  proved,  the  remedy  is 
obviously  to  change  the  areas  of  the  gas-passages,  or  to  place  baffle- 
plates  or  retard ers  in  them,  so  as  to  partially  obstruct  those  portions 
of  the  passages  where  the  gases  tend  to  travel  with  the  greatest  velocity, 
and  compel  them  to  travel  at  a  uniform  rate  across  or  along  the  whole 
extent  of  heating  surface. 

Leaks  of  Air  through  Brickwork. — If  there  are  any  large  air-leaks 
through  the  brickwork,  they  can  usually  be  discovered  by  inspection. 


BOILER  TROUBLES  AND  BOILER- USERS'   COMPLAINTS.     307 

There  are  two  methods  of  making  examinations  for  small  leaks;  first, 
passing  the  flame  of  a  candle  over  all  the  joints  of  the  brickwork  and 
noting  where  it  is  drawn  inwards  by  the  draft ;  second,  firing  a  few 
shovelsful  of  smoky  coal  while  the  damper  is  shut.  The  smoke  will 
then  be  driven  out  through  any  crevices  that  may  exist.  The  exist- 
ence of  air-leaks  in  the  brickwork  beyond  the  furnace  may  be  inferred 
from  the  results  of  a  boiler-test,  if  these  results  show  low  economy 
together  with  low  temperature  of  the  chimney-gases  and  apparently 
good  furnace-conditions,  insuring  complete  combustion.  If  the  coal 
is  thoroughly  burned  in  the  furnace,  then  low  economy  is  usually  ac- 
companied with  high  temperature  of  the  chimney-gases,  caused  either 
by  insufficient  extent  of  heating  surface  or  by  short-circuiting  of  the 
gases,  but  if  the  temperature  of  the  chimney-gases  is  low,  economy 
also  being  low  and  furnace  temperature  high,  this  would  indicate  that 
the  gases  have  been  cooled  by  the  cold  air  entering  through  leaks  in 
the  brickwork.  Chemical  analysis  of  the  gases  also  furnishes  a  means 
of  proving  the  existence  of  air-leaks.  Samples  of  gas  are  taken  sim- 
ultaneously from  a  point  near  the  furnace  and  from  a  point  near  the 
damper.  If  the  latter  sample  shows  on  analysis  a  greater  percentage 
of  free  oxygen  than  the  former,  it  proves  the  admission  of  air  into 
the  gases  between  the  points  from  which  the  two  samples  are  taken. 

If  the  supply  of  air  to  the  coal  in  the  furnace  is  sufficient  to  insure 
complete  combustion,  any  additional  supply,  either  in  the  furnace 
or  through  leaks  in  the  brickwork  into  the  gas-passages,  tends  to 
decrease  the  economy  of  the  boiler.  It  cools  the  gases,  decreasing  the 
difference  between  the  temperature  of  the  gases  and  that  of  the  water 
in  the  boiler,  upon  which  difference  the  transmission  of  heat  through 
the  heating  surface  depends,  and  the  excess  of  air-supply  finally  escapes 
at  the  temperature  of  the  chimney-gases,  thus  causing  a  direct  loss  of 
heat.  If,  however,  the  supply  of  air  in  the  furnace  is  insufficient  to 
thoroughly  burn  the  coal,  a  slight  leak  of  air  through  the  brickwork 
may  be  of  actual  benefit  in  supplying  sufficient  air  to  burn  the  un- 
burned  fuel  gases  in  the  gas-passages,  although  this  air  had  better  be 
introduced  into  the  furnace  itself. 

In  well-constructed  brickwork  settings,  with  all  cracks  in  the  joints 
carefully  plastered,  the  amount  of  loss  of  heat  due  to  leaks  of  air  is 
probably  very  small,  but  large  cracks  may  cause  a  serious  loss  of 
economy,  and  they  should  be  looked  for  carefully  and  stopped  if  found. 

Improper  Firing. — Improper  firing  is  probably  the  most  common 
of  all  the  many  causes  of  poor  economy  of  steam-boilers.  Sometimes 


308  STEAM-BOILER  ECONOMY. 

the  fact  that  an  improper  method  of  firing  is  used  can  be  learned  by 
simple  observation,  but  oftener  it  can  only  be  known  after  making  a 
series  of  systematic  experiments.  There  are  some  kinds  of  firing, 
practised  by  ignorant  or  negligent  firemen,  which  any  one  who  knows 
anything  of  the  subject  can  say  at  once  are  wrong.  Among  them  are : 
(1)  Putting  a  large  quantity  of  coal  in  the  furnace  at  a  time,  covering 
the  bed  so  thick  that  the  air-supply  is  choked  and  incomplete  combus- 
tion necessarily  takes  place.  (2)  Firing  at  irregular  intervals  and 
occasionally  allowing  the  bed  of  coal  to  burn  so  low  that  a  great 
excess  of  air  passes  through  it.  (3)  Neglecting  to  cover  the  whole  of 
the  grate  surface,  and  allowing  holes  to  form  in  the  bed  of  coal. 

There  are  other  errors  of  firing  which  are  not  evident  on  ordinary 
inspection,  which  may  be  practised  by  the  most  careful  and  intelli- 
gent firemen  without  any  suspicion  that  they  are  wrong,  and  which 
can  only  be  discovered  by  making  a  series  of  boiler-tests  or  by  analysis 
of  the  chimney-gases.  Such  errors  are  the  carrying  of  a  bed  of  coal 
either  too  thick  or  too  thin  for  the  size  of  coal  and  the  force  of  draft, 
and  unskilful  regulation  of  the  draft.  The  best  method  of  firing  is  such 
a  method  as  will  cause  the  chimney-gases  to  contain  no  carbonic  oxide, 
hydrogen,  or  hydrocarbon  gases,  and  at  the  same  time  to  contain  not 
more  than  about  S$  of  free  oxygen.  The  presence  of  combustible 
gases,  even  in  small  quantity,  in  the  chimney-gas  is  proof  of  imperfect 
combustion  and  consequent  loss  of  economy.  The  presence  of  from 
4  to  8  per  cent  of  free  oxygen  in  the  chimney-gas  is  usually  a  necessary 
accompaniment  of  complete  combustion,  but  a  greater  quantity  of  free 
oxygen  means  an  unnecessarily  large  supply  of  air,  and  consequent 
unnecessary  loss  due  to  carrying  the  excess  of  heated  air  into  the 
chimney.  The  percentage  of  carbonic  acid  in  the  gas  is  of  itself  not 
as  good  a  criterion  of  the  furnace-conditions  as  the  percentage  of 
oxygen.  If  the  percentage  of  carbonic  acid  is  13$  or  upwards,  there 
is  rarely  any  carbonic  oxide  present  and  no  great  excess  of  air,  and 
the  furnace-conditions  may  then  be  considered  as  very  good,  but  a  lower 
percentage  of  carbonic  acid  is  compatible  either  with  the  presence  of 
carbonic  oxide,  indicating  deficient  air-supply,  or  with  an  excessive 
amount  of  oxygen,  two  conditions  incompatible  with  each  other  but 
both  of  them  indicating  improper  furnace-conditions. 

Knowing  that  the  best  furnace-condition,  the  one  that  will  give 
maximum  economy,  is  one  that  will  cause  the  chimney-gases  to  con- 
tain from  4  to  8  per  cent  of  free  oxygen,  how  is  this  condition  to  be 
secured  ? 


BOILER  TROUBLES  AMD  BOILER- USERS'   COMPLAINTS.     309 

If  anthracite  coal  is  the  fuel,  there  are  at  least  three  variables 
which  enter  into  the  problem:  (1)  The  size  of  coal.  (2)  The  thick- 
ness of  bed.  (3)  The  force  of  the  draft.  If  we  consider  the  size  of 
the  coal  to  be  fixed  by  the  condition  of  the  market  price  or  other  cir- 
cumstances, then  there  are  two  variables  under  control  at  the  will  of 
the  fireman,  viz.,  the  thickness  of  bed,  and  the  force  of  the  draft. 
Sometimes  the  latter  is  beyond  his  control,  as  when  the  plant  is  being 
driven  to  its  full  capacity  and  the  draft  is  limited  by  the  size  of  the 
chimney,  the  damper  area,  the  areas  of  other  gas-passages,  etc.,  but 
this  is  a  fault  in  the  plant  which  should  not  exist.  The  chimney 
ought  always  to  have  a  capacity  for  giving  a  force  of  draft  in  excess 
of  that  ordinarily  needed,  so  that  the  draft  of  each  boiler  may  be  reg- 
ulated by  its  damper.  If  both  the  thickness  of  the  bed  and  the  force 
of  draft  are  under  control  of  the  fireman,  he  may  obtain  good  results 
with  either  thin,  thick,  or  medium  fires,  provided  the  force  of  the 
draft  is  regulated  in  proportion  to  the  thickness  of  the  fire.  'No  rule 
can  be  given  for  this  regulation  that  will  be  of  any  service.  Each 
engineer  in  charge  of  a  plant  must  determine  for  himself,  by  experi- 
ment or  observation,  the  conditions  of  thickness  of  fire  and  the  force 
of  draft  that  will  give  the  best  results  with  the  kind  of  coal  he  is 
using. 

One  general  principle  may  be  laid  down  which  it  is  important 
to  remember:  The  best  regulation  of  force  of  draft  and  of  thick- 
ness of  fire  is  that  which  makes  the  hottest  fire.  Deficient  air- 
supply,  causing  imperfect  combustion,  and  excessive  air-supply,  caus- 
ing too  great  dilution  of  the  gases  of  combustion,  both  tend  to  cool 
the  furnace.  The  hottest  fire  that  can  be  made  is  one  in  which  the 
air  is  enough  in  excess  to  insure  perfect  combustion,  but  no  more. 
The  hottest  fire  also  is  obtained  when  the  gases  of  combustion  show 
by  analysis  from  4  to  8  per  cent  of  free  oxygen,  so  that  analyses  of  the 
gases  form  an  excellent  check  on  the  working  of  the  furnace. 

In  a  plant  containing  two  or  more  boilers  connected  with  a  single 
horizontal  flue  leading  to  the  chimney,  unless  the  draft  of  each  is 
carefully  regulated  by  a  damper,  the  force  of  draft  at  each  of  the  dif- 
ferent boilers  may  greatly  vary.  If  the  force  of  draft  at  the  several 
boilers  cannot  be  equalized,  then  the  thickness  of  coal-bed  under  each 
boiler  should  be  regulated  in  proportion  to  the  draft  of  each. 

The  attention  to  the  proper  regulation  of  the  thickness  of  the  bed 
of  coal  to  the  force  of  the  draft,  which  is  here  recommended,  may 
seem  to  be  an  unnecessary  refinement,  involving  more  trouble  thau 


310  STEAM-BOILER  ECONOMY. 

any  value  that  may  be  gained  from  it,  but  if  a  saving  of  only  1  or  2 
per  cent  may  be  made  thereby,  is  it  not  worth  the  trouble  ? 

There  are  almost  no  records  of  experiments  available  to  show  the 
relative  results  obtained  by  different  methods  of  firing  anthracite  coal, 
but  there  are  hundreds  of  records  of  tests  with  anthracite  coal  showing 
differences  of  economy  of  over  20$,  which  differences  are  not  satisfac- 
torily explained  by  differences  in  the  type  or  proportions  of  boiler,  in 
kind  of  coal,  rate  of  driving,  or  in  anything  else  in  the  record.  It  is 
highly  probable  that  many  of  the  low  results  are  due  to  improper  reg- 
ulation of  the  thickness  of  the  fire.  If  such  low  results  are  obtained 
in  boiler-tests,  in  which  efforts  are  made  to  obtain  good  results,  it  is 
probable  that  much  lower  results  are  obtained  in  every-day  practice,  in 
which  boilers  are  fired  year  in  and  year  out  without  any  tests  being 
made  to  determine  their  economy. 

A  notable  result  of  the  loss  due  to  improper  firing  is  shown  in  the 
report  of  Prof.  Walter  K.  Johnson  of  the  tests  he  made  for  the  United 
States  Navy  Department  in  1842  and  1843.*  He  tested  seven  differ- 
ent anthracite  coals,  six  of  them  giving  an  evaporation  ranging  from 
11.15  to  .11.59  pounds,  averaging  11.42  pounds  of  water  from  and  at 
212°  per  pound  of  combustible,  and  the  seventh,  a  Lehigh  coal,  only 
10.20  pounds,  or  over  10$  less  than  the  average  of  the  other  six  coals. 
Prof.  Johnson,  in  his  report,  gives  no  hint  of  the  real  reason  why  the 
Lehigh  coal  gave  such  a  low  figure,  but  he  gives  an  analysis  of  the 
chimney-gases  which  shows  the  extremely  low  figure  of  4.57  for  the 
percentage  of  carbonic  acid,  and  the  very  high  figure  of  16.7  for  the 
percentage  of  oxygen.  From  this  analysis  he  calculates  that  47.9 
pounds  of  air  were  required  to  burn  1  pound  of  the  fuel,  an  amount 
which  is  more  than  double  that  required  to  burn  the  other  coals. 
He  says  that  the  large  proportion  of  unchanged  air  in  the  chimney- 
gases  is  probably  due  in  some  degree  to  the  obstruction  which  the  air 
meets  in  arriving  at  the  surface  of  the  coal,  from  the  coat  of  ashes 
which  covers  its  surface  during  its  combustion.  He  explains  the  ex- 
istence of  this  coat  of  ashes  forming  on  this  coal  more  than  on  all 
others,  as  being  due  to  the  purity  of  the  ashes  themselves,  which 
hinders  their  vitrification  and  flowing  away. 

The  true  reason  of  Prof.  Johnson's  low  results  with  this  Lehigh 
coal  is  no  doubt  that  he  used  too  thin  a  bed  of  coal  on  the  grate  for 
the  amount  of  draft  he  had.  The  rate  of  combustion  was  very  low, 

*  Engineering  and  Mining  Journal,  October  24  and  31,  1891. 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     311 

€.52  to  7.71  pounds  of  coal  per  square  foot  of  grate  per  hour,  or  only 
lialf  of  that  commonly  used  in  good  modern  practice.  If  he  had 
attempted  to  increase  the  rate  of  combustion  by  increasing  the  draft, 
leaving  the  thickness  of  the  bed  the  same,  he  might  have  chilled  the 
lire  so  as  to  put  it  out,  but  if  he  had  thickened  the  bed  so  as  to  offer 
more  obstruction  to  the  passage  of  air  through  it,  he  might  have  ob- 
tained from  the  Lchigh  coal  as  good  a  result  as  he  did  with  other 
coals,  which  themselves  are  not  as  high  as  those  obtained  iu  several  of 
the  tests  with  anthracite  coal  at  the  Centennial  Exhibition. 

The  difficulties  met  with  in  obtaining  the  proper  proportion  of 
thickness  of  bed  to  force  of  draft  with  anthracite  coal  are  increased 
when  we  have  to  deal  with  bituminous  coal,  since  there  are  other 
variables  in  the  problem  besides  those  of  size  of  coal,  thickness  of  bed, 
-and  force  of  draft.  Chief  of  these  is  probably  the  varying  rate  of 
distillation  of  moisture  and  volatile  matter,  which  exists  Tiot  only 
with  different  coals,  but  with  the  same  coal  during  the  intervals  be- 
tween firings.  With  the  highly  volatile  coals  of  Illinois,  when  fired 
by  hand,  a  perceptible  change  in  the  furnace  conditions  is  made  every 
minute.  Immediately  after  firing,  the  supply  of  air  through  the 
grates  is  too  little  to  burn  the  gases  that  are  being  distilled;  a  few 
minutes  later,  when  the  gases  have  all  been  driven  off,  the  air-supply 
is  apt  to  be  excessive,  and  this  supply  increases  the  longer  the  time 
which  elapses  until  the  next  firing.  With  such  coals,  burned  in  ordi- 
nary furnaces,  with  hand-firing,  it  is  scarcely  possible  to  obtain  an 
efficiency  as  high  as  60$  of  the  heating  value  of  the  coal,  while  with 
anthracite  coal  75$  is  not  uncommon.  By  a  series  of  experiments, 
checked  by  analyses  of  the  chimney-gases,  it  is  possible  to  arrive  at 
almost  ideal  furnace  conditions,  and  hence  to  discover  the  proper 
method  of  firing  of  anthracite  coal,  but  with  bituminous  coal  it  is 
impossible;  and  hence,  with  this  latter  coal  in  ordinary  furnaces  all 
kinds  of  firing  by  hand  are  improper;  some  may  be  worse  than  others, 
but  they  are  all  bad.  Millions  of  tons  of  coal  are  wasted  every  year 
in  the  bituminous  coal  districts  by  improper  kinds  of  furnaces  and 
improper  firing.  Remedies,  however,  are  available  in  improved  styles 
of  furnace  and  in  mechanical  stoking. 

Insufficient  Heating  Surface. — A  common  complaint  made  by  the 
purchaser  of  a  new  steam-boiler  is  "  The  boiler  does  not  make  enough 
steam."  The  complaint  requires  an  immediate  investigation,  and  an 
evaporation  test  should  be  made  to  determine  how  much  steam  it 
actually  makes.  The  boiler  has  probably  been  guaranteed  to  make  a 


312  STEAM-BOILER  ECONOMY. 

certain  amount,  say  3  or  4  pounds  per  hour  for  each  square  foot  of 
heating  surface.  If  the  test  shows  that  it  makes  less  than  this  amount,, 
the  trouble  will  usually  be  found  to  be  not  insufficient  heating  sur- 
face, but  either  deficient  draft,  insufficient  gnite  surface  for  the  kind 
of  coal  used  and  for  the  draft  available,  choking  up  the  grate  by 
clinker,  or  short-circuiting  of  the  gases.  The  remedies  to  be  applied 
are  such  as  will  insure  the  burning  of  sufficient  coal  and  such  an 
arrangement  of  the  gas-passages  as  will  prevent  the  short-circuiting. 
If,  however,  the  boiler  is  found  to  be  evaporating  the  amount  of  water 
guaranteed,  the  seller  is  relieved  of  his  responsibility,  and  he  may 
properly  tell  the  purchaser  that  the  heating  surface  is  insufficient,  or 
in  other  words  that  the  purchaser  bought  too  small  a  boiler.  Tha 
purchaser  may  reply  to  this  that  he  has  other  boilers  which  are  evap- 
orating from  6  to  8  pounds  of  water  per  hour  per  square  foot  of  heating 
surface,  and  an  evaporation  test  may  show  that  his  statement  is  correct. 
It  is  very  apt  to  show  also,  however,  that  the  boilers  which  are  driven 
at  this  rate  are  wasting  fuel  by  being  overdriven.  The  purchaser 
then  has  the  option  of  taking  means,  such  as  increasing  the  area  of 
"the  grate  surface  and  the  force  of  draft,  which  will  cause  the  new 
boiler  to  burn  more  coal  and  so  drive  it  up  to  the  rate  of  6  or  8  pounds 
per  hour  per  square  foot  of  heating  surface,  thus  wasting  coal,  or  of 
buying  additional  boilers  sufficient  to  give  the  required  amount  of 
steam  at  the  rate  of  3  or  4  pounds,  and  thus  saving  fuel.  Whether  he 
will  do  the  one  or  the  other  will  depend  on  the  price  of  coal  and 
whether  the  saving  will  warrant  the  extra  investment.  The  general 
relation  of  rate  of  driving  to  economy  of  fuel  varies  so  greatly  witli 
different  circumstances  that  it  is  advisable  in  each  case  of  the  kind 
under  consideration  to  make  a  series  of  tests  to  determine  this  relation 
for  a  particular  plant  before  deciding  whether  to  purchase  additional 
boilers  or  to  drive  those  already  in  place  at  a  more  rapid  rate. 

If  a  test  is  made  of  each  boiler  in  the  plant  under  regular  working- 
conditions  it  will  sometimes  be  found  that  no  two  of  the  boilers  are- 
driven  at  the  same  rate,  and  that  an  equalizing  or  regulation  of  the 
draft  at  the  several  boilers  will  effect  an  important  saving  of  fuel  and 
may  increase  the  total  capacity  so  as  to  make  the  purchase  of  addi- 
tional boilers  unnecessary.  The  author  once  made  a  test  of  three- 
boilers  in  the  same  plant.  The  first  was  a  long  distance  from  tha 
chimney;  it  had  a  small  grate  and  large  heating  surface,  and  the  draft 
was  insufficient  to  cause  it  to  develop  its  rated  capacity.  The  second 
had  a  very  large  grate  surface,  was  close  to  the  chimney,  had  a  power- 


BOILER  TROUBLES  AND  BOILER- USERS'   COMPLAINTS.     3  la 

ful  draft,  and  was  developing  double  its  rating,  while  wasting  30$  of 
the  fuel  as  compared  with  the  other  boilers.  The  third  was  between 
the  other  two  in  location;  the  size  of  grate  and  draft  were  so  related 
to  each  other  that  it  developed  a  little  more  than  its  rating  and  gave 
a  very  high  economy.  The  evident  remedy  in  this  case  was  to  cut. 
down  the  grate  surface  and  check  the  draft  in  the  second  boiler,  and 
to  increase  both  the  grate  surface  and  the  draft  in  the  first  boiler.. 
The  total  horse-power  developed  by  the  three  boilers  would  then  be 
the  same,  but  about  10$  of  the  fuel  would  have  been  saved,  and  by 
then  increasing  the  draft  on  all  the  boilers  a  greater  horse-power 
could  be  developed  with  the  original  consumption  of  fuel. 

Insufficient  heating  surface  is  a  most  serious  evil,  and  it  is  often 
unsuspected  if  evaporation  tests  are  not  made  It  is  always  the  cause 
of  waste  of  fuel,  but  if  the  boilers  give  all  the  steam  that  is  desired, 
the  grate  surfaces,  draft  and  quality  of  coal  being  such  that  the  boilers 
may  be  driven  far  beyond  their  economical  rating,  their  waste  of  fuel 
may  never  be  discovered,  because  they  are  never  tested. 

Bad  Water. — The  troubles  arising  from  the  character  of  the  water 
used  for  steam-boilers  are  of  two  different  kinds:  1,  corrosion;  2,  in- 
crustation, or  scale.  Sometimes  both  troubles  exist  at  the  same  time. 

Corrosion  is  due  to  the  presence  in  the  water  of  some  oxidizing 
agent,  such  as  air,  carbonic  acid  gas,  free  acids,  or  dissolved  salts,  such 
as  magnesium  chloride,  which  have  a  corrosive  action  upon  iron  and 
steel.  The  purest  waters,  such  as  rain-water  and  melted  snow,  gener- 
ally contain  dissolved  gases,  and  sometimes  sulphuric  acid,  obtained 
from  the  atmosphere  in  localities  where  great  quantities  of  coal  con- 
taining sulphur  are  burned,  and  these  waters  if  used  in  boilers,  the 
inner  surfaces  of  which  are  clean  and  unprotected  by  a  coating  of 
scale,  may  cause  pitting  of  the  plates,  or  more  or  less  general  corro- 
sion. The  corrosion  produced  by  such  waters  may  usually  be  pre- 
vented by  occasionally  adding  a  little  milk  of  lime  to  the  water,  just 
enough  to  cause  a  very  thin  coating  of  scale  upon  the  plates.  Pitting, 
which  is  due  to  dissolved  gases,  occurs  when  the  boiler  is  merely  warm 
to  a  much  greater  extent  than  when  it  is  hot  and  in  service.  When  a 
boiler  is  to  be  kept  out  of  service  for  any  length  of  time,  particular 
care  should  be  taken  to  insure  that  the  water  in  it,  if  it  has  any  cor- 
rosive tendency,  should  be  neutralized  by  the  addition  of  milk  of 
lime. 

Distilled  water,  such  as  that  obtained  from  the  returns  of  steam- 
heating  systems,  in  which  exhaust  steam  is  used,  and  from  surface- 


314  STEAM-BOILER  ECONOMY. 

condensers,  is  also  apt  to  be  corrosive,  due  to  the  accumulation  in  it 
of  fatty  acids  generated  by  the  decomposition  of  the  vegetable  or 
animal  oils,  which  are  often  used  in  "  compounded  "  lubricating  oils. 
When  such  water  is  used,  the  oil  should  be  removed  from  it  as  much  as 
possible  before  it  enters  the  boiler,  and  the  acid  should  be  neutralized 
by  the  addition  of  a  very  small  amount  of  alkali. 

A  much  more  important  and  more  dangerous  cause  of  corrosion 
than  those  above  mentioned  is  the  use  of  water  containing  free  sul- 
phuric acid,  or  acid  salts,  such  as  is  often  found  in  streams  in  the 
vicinity  of  coal-mines,  or  in  streams  polluted  by  the  .discharge  into 
them  of  refuse  from  dye-works,  chemical-factories,  and  other  manu- 
facturing establishments.  When  such  water  is  the  only  kind  available 
for  a  steam-boiler,  then  it  is  necessary,  in  order  to  prevent  its  corrod- 
ing the  boiler,  to  neutralize  the  acid  by  adding  an  alkali,  such  as  car- 
bonate of  soda,  to  the  water.  The  presence  of  acid  in  the  water  in  a 
boiler  may  be  tested  by  drawing  a  small  sample  from  the  bottom 
.gauge-cock  and  inserting  into  it  a  piece  of  blue  litmus  paper,  which 
may  be  obtained  at  a  drug-store.  If  there  is  free  acid  in  the  water 
the  blue  color  in  the  paper  will  be  changed  to  red.  By  adding  alkali 
to  the  acid  water,  drop  by  drop,  and  stirring  thoroughly,  the  red  color 
will  be  changed  back  to  blue  as  soon  as  the  alkali  becomes  in  excess. 
In  order  to  determine  the  quantity  of  carbonate  of  soda  which  should 
be  added  to  acid  feed-water  to  neutralize  the  acid,  a  pint  of  it  may  be 
taken  from  the  supply-pipe  (not  from  the  boiler,  as  there  the  acid  may 
have  become  concentrated  by  evaporation),  and  a  strip  of  blue  litmus 
paper  be  immersed  in  it  for  half  its  length,  and  allowed  to  remain  a 
minute  or  two.  The  blue  color  of  the  wetted  portion  will  change  to 
purple  if  the  water  is  very  slightly  acid,  and  to  red  if  it  is  more  strongly 
acid.  Then  add  carefully  a  solution  of  carbonate  of  soda,  say  1  ounce 
dissolved  in  a  quart  of  water,  until  the  purple  color  begins  to  change 
to  blue  or  the  red  to  purple.  Measuring  the  quantity  of  the  solution 
which  has  been  required  to  effect  the  slightest  change  of  color  gives  us 
a  means  of  estimating  the  amount  of  carbonate  of  soda  which  is  needed 
to  neutralize  the  acid  in  a  given  amount  of  acid  feed- water,  and  make 
it  slightly  alkaline.  When  the  water  is  exactly  neutral,  it  will  not 
change  the  color  of  either  red  or  blue  litmus  paper.  When  the  pro- 
portion of  alkaline  water  of  a  known  strength  required  to  neutralize 
the  acid  in  the  feed-water  has  thus  been  determined,  it  may  be  added 
to  the  water  either  in  the  supply-tank,  or  pipe,  in  the  feed-water 
heater,  or  in  the  boiler,  as  may  be  most  convenient.  When  a  feed- 


BOILER   TROUBLES  AND  BOILER-USERS'   COMPLAINTS.  315 

water  heater  is  used  the  alkali  should  be  added  either  in  it  or  in  the 
.supply  before  the  water  reaches  the  heater,  for  if  not  added  until  after 
the  water  passes  the  heater,  the  acid  will  corrode  the  heater.  It  is 
better  always  to  add  the  alkali  in  the  supply- tank,  for  the  acid  is  apt 
to  corrode  the  pump  arid  the  pipes,  as  well  as  the  heater  and  the 
boiler. 

When  the  feed -water  contains  simply  free  acid  without  any  impor- 
tant amount  of  scale-forming  material,  such  as  lime  or  magnesia,  the 
treatment  by  carbonate  of  soda  is  usually  all  that  is  necessary,  but 
if  lime  or  magnesia  or  both  are  present,  the  treatment  becomes  a 
more  complicated  matter,  and  it  is  then  most  desirable  to  call  in  the 
services  of  a  chemist  who  is  expert  in  the  treatment  of  bad  feed-waters 
and  take  his  advice  as  to  the  method  of  purification  to  be  adopted. 
In  such  cases  it  will  usually  be  necessary  to  use  large  settling-tanks, 
adding  caustic  lime  or  carbonate  of  soda,  or  both,  for  precipitating  and 
settling  out  the  hydrate  or  carbonate  of  lime  formed  by  the  chemical 
reaction,  or  else  to  use  a  live-steam  feed-water  heater,  after  neutraliz- 
ing the  water  with  carbonate  or  caustic  soda,  in  which  the  scale- 
forming  materials  will  be  deposited.  It  is  necessary  ahvays  to  avoid 
using  an  excess  of  soda  or  other  alkali,  for  such  excess  is  apt  to  cause 
foaming.  As  the  quality  of  the  water  is  apt  to  vary  from  time  to  time, 
the  impurities  diminishing  in  rainy  seasons  and  increasing  in  times  of 
drought,  it  is  advisable  to  have  tests  of  the  water  made  frequently, 
and  to  vary  the  amount  of  reagents  used  in  accordance  with  the  results 
of  these  tests.  Organic  matter,  contained  in  sewage  or  in  water  from 
swamps,  peat-bogs,  etc.,  is  sometimes  a  cause  of  corrosion,  which  may 
be  prevented  by  proper  chemical  treatment. 

Kerosene  oil,  which  is  sometimes  used  as  a  scale  preventive,  is  said 
to  be  sometimes  a  cause  of  corrosion,  due  to  the  fact  that  the  oil  may 
•contain  traces  of  the  sulphuric  acid  which  was  used  in  its  purification. 
Water  containing  chloride  of  magnesium  is  apt  to  be  corrosive, 
since  this  salt  decomposes  at  high  temperatures,  liberating  free  acid. 
The  acid  may  be  neutralized  by  carbonate  of  soda. 

Weakening  of  the  plates  by  corrosion  is  one  of  the  greatest  dangers 
to  which  boilers  are  liable,  and  it  should  be  guarded  against  by  fre- 
quent and  thorough  inspection  of  the  interior  by  a  competent  inspec- 
tor, and  whenever  it  is  found  no  expense  should  be  spared  to  prevent 
its  continuance.  If  the  corrosion  is  trifling  in  amount,  some  simple 
remedy  may  usually  be  found,  such  as  rendering  the  water  slightly 
alkaline  by  lime-water  or  carbonate  of  soda. 


316  STEAM-BOILER  ECONOMY. 

Sometimes  a  remedy  is  found  in  hanging  zinc  plates  in  the  water  in 
the  boiler,  suspending  them  by  wires  or  rods  which  are  soldered  to  the 
upper  part  of  the  shell,  so  as  to  make  an  electric  connection,  the  zinc, 
the  steel  plates  of  the  boiler  and  the  corrosive  water  thus  forming  a, 
galvanic  battery,  the  zinc  being  eaten  away  and  the  iron  being  thus 
protected. 

The  following  note  on  the  use  of  zinc  is  taken  from  a  report  by  the 
Committee  on  Boilers  of  the  Institution  of  Mechanical  Engineers 
(1884) : 

Of  all  the  preservative  methods  adopted  in  the  British  service,  the- 
use  of  zinc  properly  distributed  and  fixed  has  been  found  the  most 
effectual  in  saving  the  iron  and  steel  surfaces  from  corrosion,  and  also 
in  neutralizing  by  its  own  deterioration  the  hurtful  influences  met 
with  in  water  as  ordinarily  supplied  to  boilers.  The  zinc  slabs  now 
used  in  the  navy  boilers  are  12  in.  long,  6  in.  wide,  and  ^  in.  thick;; 
this  size  being  found  convenient  for  general  application.  The  amount 
of  zinc  used  in  new  boilers  at  present  is  one  slab  of  the  above  size  for 
every  20  I.H.P.,  or  about  one  square  foot  of  sine-surface  to  two  square- 
feet  of  grate-surface.  Rolled  zinc  is  found  the  most  suitable  for  the- 
purpose.  To  make  the  zinc  properly  efficient  as  a  protector  especial 
care  must  be  taken  to  insure  perfect  metallic  contact  between  the 
slabs  and  the  stays  or  plates  to  which  they  are  attached.  The  shibs 
should  be  placed  in  such  positions  that  all  the  surfaces  in  the  bciler 
shall  be  protected.  Each  slab  should  be  periodically  examined  to  see 
that  its  connection  remains  perfect,  and  to  renew  any  that  may  have 
decayed;  this  examination  is  usually  made  at  intervals  not  exceeding 
three  months.  Under  ordinary  circumstances  of  working  these  zinc 
slabs  maybe  expected  to  last  in  fit  condition  from  sixty  to  ninety  days 
immersed  in  hot  sea-water;  but  in  new  boilers  they  at  first  decay  more 
rapidly.  The  slabs  are  generally  secured  by  means  of  iron  straps  2  in^ 
wide  and  f  in.  thick,  and  long  enough  to  reach  the  nearest  stay,  to- 
which  the  strap  is  firmly  attached  by  screw-bolts. 

On  the  same  subject  The  Locomotive  says: 

Zinc  is  often  used  in  boilers  to  prevent  the  corrosive  action  of 
water  on  the  metal.  The  action  appears  to  be  an  electrical  one,  the- 
iron  being  one  pole  of  the  battery  and  the  zinc  being  the  other.  The 
hydrogen  goes  to  the  iron  shell  and  escapes  as  a  gas  into  the  steam. 
The  oxygen  goes  to  the  zinc. 

On  account  of  this  action  it  is  generally  believed  that  zinc  will, 
always  prevent  corrosion,  and  that  it  cannot  be  harmful  to  the  boiler 
or  tank.  Some  experiences  go  to  disprove  this  belief,  and  in  numer- 
ous cases  zinc  has  not  only  been  of  no  use,  but  has  even  been  harmful. 
In  one  case  a  tubular  boiler  had  been  troubled  with  a  deposit  of  scale- 
consisting  chiefly  of  organic  matter  and  lime,  and  zinc  was  tried  as  a, 
preventive.  The  beneficial  action  of  the  zinc  was  so  obvious  that  its, 
continued  use  was  advised,  with  frequent  opening  of  the  boiler  and 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     317 

cleaning  out  of  detached  scale  until  all  the  old  scale  should  be  re- 
moved and  the  boiler  become  clean.  Eight  or  ten  months  later  the 
water-supply  was  changed,  it  being  now  obtained  from  another  stream 
supposed  to  be  free  from  lime  and  to  contain  only  organic  matter. 
Two  or  three  months  after  its  introduction  the  tubes  and  shell  were 
found  to  be  coated  with  an  obstinate  adhesive  scale,  composed  of  zinc 
oxide  and  the  organic  matter  or  sediment  of  the  water  used.  The 
deposit  had  become  so  heavy  in  places  as  to  cause  overheating  and 
bulging  of  the  plates  over  the  fire. 

If  the  corrosion  is  serious  it  may  be  necessary  either  to  change  the 
feed-water  or,  if  this  is  not  practicable,  to  treat  it  with  chemicals  in 
tanks  and  filter  it  before  allowing  it  to  enter  the  boiler. 

Grooving  or  channelling  is  a  kind  of  local  corrosion,  usually  found 
adjacent  to  the  seams  of  the  shell  of  a  boiler.  It  is  commonly  due  to 
a  combination  of  slightly  acidulated  water  and  of  strains  in  the  boiler- 
shell  due  to  expansion  and  contraction,  which  cracks  the  scale  off  the 
shell  and  exposes  the  clean  metal.  It  is  an  extremely  dangerous  form 
of  corrosion,  and  calls  for  an  immediate  remedy. 

Incrustation  and  Scale. — The  formation  of  scale  is  the  most  com- 
mon of  all  boiler  troubles.  It  is  due  to  the  presence  in  the  feed-water 
of  various  substances,  some  of  which,  such  as  clay  and  finely  divided 
vegetable  or  organic  matter,  are  carried  in  suspension  and  others  are 
carried  in  solution.  Of  the  substances  that  are  held  in  solution, 
some,  such  as  carbonate  of  lime,  are  precipitated  by  heating  to  a  tem- 
peniture  of  212°;  others,  such  as  sulphate  of  lime,  are  precipitated  to 
some  extent  at  higher  temperatures.  Still  others,  such  as  common 
salt,  cannot  be  precipitated  at  all,  but  remain  in  solution  until  enough 
water  is  evaporated  away  to  cause  the  solution  to  become  saturated ; 
that  is,  holding  the  greatest  possible  quantity  of  salt  in  solution,  when 
the  salt  begins  to  crystallize,  and  it  will  then  rapidly  form  a  coating 
on  the  boiler-surfaces. 

When  the. scale-forming  material  is,  like  common  salt,  incapable  of 
being  precipitated  by  heating,  but  capable  of  forming  solid  masses  by 
concentration  and  crystallization,  it  may  to  some  extent  be  prevented 
from  forming  scale  by  frequent  blowing  off,  so  as  to  keep  the  strength 
•of  the  brine  below  the  saturation-point.  This  was  the  old  practice 
with  marine  boilers  using  sea-water,  before  surface-condensers  and 
feod-water  evaporators  came  into  use.  It  is  still  the  only  method  by 
which  salt  water  can  be  used  in  a  steam-boiler.  Sea-water,  however, 
contains  sulphate  of  lime  and  other  impurities  which  will  be  pre- 
cipitated and  make  scale  at  high  temperatures. 


318  STEAM-BOILER  ECONOMY. 

When  the  scale-forming  material  is  carried  in  suspension  in  the 
water,  whether  in  the  original  cold  feed-water,  as  in  the  case  of  clay 
in  muddy  water,  or  in  fine  particles  precipitated  by  heat  in  the  feed- 
water  heater  or  in  the  boiler,  or  by  the  addition  of  chemicals,  the 
evaporation  of  the  water  in  the  boiler  will  cause  this  material  to  accu- 
mulate, and  it  will  give  rise  to  trouble  unless  it  is  removed.  It  is  apt 
to  take  any  one  of  three  forms;  sometimes  all  three  of  them  may  be 
formed  from  the  same  water.  The  first  is  scum,  which  floats  on  top 
of  the  water,  and  may  be  removed  by  a  scum-collector  and  a  surface 
blow-off.  The  second  is  soft  mud,  which,  while  it  is  in  a  very  soft, 
almost  liquid  condition,  may  be  blown  out  through  the  blow-off  valve, 
or  when  the  boiler  is  laid  off  for  cleaning  may  be  washed  out  with  a 
jet  of  water  from  a  hose.  The  third  is  solid  scale,  ranging  from 
a  soft  chalk  which  may  easily  be  broken  by  the  fingers,  to  hard 
cement  or  a  porcelain-like  substance  which  it  is  difficult  to  break  or 
cut  by  a  hammer  and  chisel. 

The  scum,  which  at  first  floats  on  the  surface,  will,  if  allowed  to* 
accumulate,  sink  and  be  deposited  on  the  tubes  or  shell  of  the  boiler,, 
and  will  become  either  mud  or  scale.  The  mud,  which  may  be  washed 
out  of  the  boiler,  may  also  become  cemented  by  the  other  substances 
precipitated  from  the  water,  or  may  be  baked  on  the  shell.  Scale 
attaches  itself  to  all  the  metal  surfaces  of  the  boiler,  including  tubes, 
rivet-heads,  braces,  etc.,  as  well  as  to  the  shell. 

The  effect  of  scale  in  a  boiler  ordinarily  is  to  reduce  both  its  steam- 
generating  capacity  and  its  economy,  since  it  is  not  a  good  conductor 
of  heat,  and  therefore  diminishes  the  transmission  of  heat  through  the 
plates.  It  is  also  often  highly  dangerous,  whenever  it  accumulates  to 
such  an  extent,  at  a  part  of  the  shell  which  is  exposed  to  flame,  or  to 
very  hot  gases,  that  the  plates  become  overheated  and  weakened.  A 
thin  scale  may  form  on  the  tubes,  be  cracked  off  by  their  expansion 
and  contraction,  or  detached  by  the  action  of  some  "boiler  com- 
pound," and  may  then  be  carried  by  the  circulation  and  deposited  in 
a  thick  mass  on  the  shell  over  the  fire.  This  may  cause  a  "  bagged  " 
plate,  or  a  crack  and  an  'explosion. 

The  amount  of  the  loss  of  economy  due  to  scale-deposit  is  often 
overestimated.  We  frequently  see  statements  published  to  the  effect 
that  scale  T1T  inch  thick  will  increase  the  quantity  of  fuel  required  by 
a  boiler  15  per  cent,  J  inch  60  per  cent,  etc.,  but  there  seems  to  be  no 
experimental  basis  for  this  statement.  It  is  probable  that  the  de- 


BOILER   TROUBLES  AND  BOILER-USERS'    COMPLAINTS. 

crease  of  heat  transmitted  depends  upon  the  kind  of  scale  as  well  as 
upon  its  thickness,  and  that  it  is  not  proportional  to  the  thickness, 
but  increases  at  a  slower  rate.  If  the  scale  is  dense  and  hard,  so  as  to 
be  practically  waterproof,  a  thin  coating  of  it  may  be  an  effective  non- 
conductor, and  it  may  be  a  source  of  great  danger  as  well  as  of  loss 
of  economy.  If,  however,  it  is  porous,  as  many  scales  are,  it  wjll  allow 
water  to  pass  through  it  to  the  metal  surfaces  of  the  boiler,  and  the 
decreased  transmission  of  heat  will  be  very  slight.  The  author  once 
made  a  test  of  a  water-tube  boiler  which  had  a  coating  of  scale 
throughout  its  whole  heating  surface  of  about  i  inch  thick,  and  ob- 
tained practically  the  same  evaporation  as  he  obtained  a  few  days  later 
after  the  boiler  had  been  cleaned.  This  is  only  one  case,  but  tha 
result  is  not  unreasonable  when  it  is  known  that  the  scale  was  very 
soft  and  porous,  and  was  easily  removed  from  the  tubes  by  scraping. 

The  methods  of  treatment  adopted  for  the  removal  or  prevention 
of  scale  are  numerous.  The  most  common,  perhaps,  is  to  allow  it  to 
accumulate  in  the  boiler  until  it  is  thought  to  be  thick  enough  to  be  a 
source  of  danger,  or  of  loss  of  economy,  and  then  to  remove  it  by 
mechanical  means.  This  may  be  a  good  enough  method  in  some  cases, 
especially  when  the  water  is  not  very  bad,  so  that  it  requires  several 
months  for  a  coating  of  objectionable  thickness  to  form,  when  the- 
scale  is  of  such  a  nature  that  it  does  not  detach  itself  and  accumulate 
in  thick  patches  over  the  fire,  and  when  the  boiler  is  of  such  a  con- 
struction that  it  is  possible  to  clean  it  thoroughly,  such  as  a  water-tube 
boiler  with  straight  tubes. 

Another  method,  commonly  used,  is  to  introduce  periodically  into 
the  boiler  a  solution  of  some  chemical,  such  as  caustic  soda,  tannate, 
carbonate  and  phosphate  of  soda,  etc.,  which  will  cause  a  change  in 
the  chemical  composition  of  the  scale-forming  material,  making  a  pre- 
cipitate which  may  be  easily  removed  and  a  soluble  material  which 
may  be  kept  below  the  point  of  concentration  by  occasional  blowing 
off. 

These  chemicals  form  the  base  of  many  of  the  "  boiler  compounds," 
some  of  which  may  cure  the  disease,  while  many  will  not,  although 
they  are  sold  at  a  very  high  price  compared  with  the  market  value  of 
the  chemicals.  In  relation  to  these  compounds  Mr.  Albert  A.  Gary 
says: 

Never  use  any  boiler  compound  unless  you  know  positively  just 
what  it  is  composed  of,  and  how  it  will  affect  the  impurities  in  your 
boiler  and  the  boiler  itself.  In  the  treatment  of  boiler-waters,  always 


-'320  STEAM-BOILER  ECONOMY. 

;start  with  a  careful  analysis  of  the  water,  made  by  a  competent  chem- 
ist who  has  experience  in  this  line.  Next,  if  you  are  thinking  of  using 
.any  chemical  that  has  been  offered  for  treatment  of  your  boiler-water, 
let  your  chemist  analyze  it.  If  you  are  dealing  with  straightforward 
people,  they  will  generally  tell  you  the  exact  composition  of  their 
material,  which  your  chemist  can  verify  easily,  after  which  he  will 
be  prepared  to  advise  properly.  (Engineering  Magazine,  June,  1897.) 

In  1885  a  report  made  by  the  Bavarian  Steam-boiler  Inspection 
Association  gave  a  list  of  twenty-seven  boiler  compounds  which  had 
-been  analyzed.  It  commented  on  them  as  follows: 

All  secret  compounds  for  removing  boiler-scale  should  be  avoided. 
Such  secret  preparations  are  either  nonsensical  or  fraudulent,  or  con- 
tain either  one  of  the  two  substances  (soda  or  lime)  recommended  by 
the  Association  for  removing  scale,  generally  soda,  which  is  colored 
to  conceal  its  presence,  and  sometimes  adulterated  with  useless  or  even 
injurious  matter.  These  additions,  as  well  as  giving  the  compound 
some  strange,  fanciful  name,  are  meant  simply  to  deceive  the  boiler- 
owner  and  conceal  from  him  the  fact  that  he  is  buying  colored  soda, 
or  similar  substances,  for  which  he  is  paying  an  exorbitant  price. 

Besides  the  methods  of  removing  the  scale  after  it  has  encrusted 
the  boiler,  and  preventing  its  formation  by  means  of  chemicals  intro- 
duced into  the  boiler  and  frequent  blowing  off,  there  are  many  ways 
of  treating  water  to  remove  its  scale-forming  material  before  allowing 
it  to  enter  the  boiler.  A  common  method,  and  for  some  kinds  of 
water  one  of  the  best,  is  to  heat  the  water  in  an  open  feed-water  heater. 
If  the  scale-forming  material  is  simply  bicarbonate  of  lime,  that  is, 
mono-carbonate  held  in  solution  by  carbonic-acid  gas  dissolved  in  the 
water,  it  may  be  almost  entirely  precipitated  by  continued  heating  to 
drive  off  the  carbonic-acid  gas.  The  insoluble  carbonate  thus  precipi- 
tated will  attach  itself  to  the  plates  of  the  heater,  which  therefore 
needs  to  be  cleaned  frequently.  Even  sulphate  of  lime  can  be  precipi- 
tated to  a  considerable  extent  by  heating  it  to  about  300°  in  a  live- 
steam  feed-water  heater,  such  as  the  Hoppes. 

When  the  water  is  very  bad,  the  feed-water  heaters  may  prove  in- 
sufficient to  purify  it,  and  then  recourse  must  be  had  to  treatment  of 
the  water  by  chemicals  in  tanks,  and  subsequent  slow  settling  or 
filtration  to  remove  the  sediment  formed.  Hydrate  or  milk  of  lime, 
•carbonate  of  soda  and  caustic  soda  are  the  chemicals  used.  This 
method  requires  a  somewhat  expensive  equipment,  and  great  care  in 
its  operation.  It  should  not  be  undertaken  without  competent  expert 
advice  together  with  chemical  analysis. 


BOILER   TROUBLES  AND  BOILER-USERS'    COMPLAINTS.     321 

Kerosene  oil,  and  other  refined  petroleum  oils,  heavier  than  kero- 
sene, are  sometimes  used  with  good  effect  in  boilers  to  prevent  the 
scale-forming  materials  attaching  themselves  to  the  boiler.  These 
oils  appear  to  rot  the  scale  so  that  it  may  easily  be  removed.  Crude 
oil  should  never  be  used,  as  it  gives  off  inflammable  vapors,  and  leaves 
a  tarry  residuum  which  may  form  with  the  scale  a  tough,  greasy  de- 
posit on  the  plates  over  the  fire  and  cause  them  to  burn  out. 

A  condensed  summary  of  the  various  causes  of  incrustation,  cor- 
rosion, etc.,  and  their  remedies,  is  given  as  follows  in  a  paper  by 
Messrs.  A.  E.  Hunt  and  G.  H.  Clapp,  in  the  Transactions  of  the 
American  Society  of  Mechanical  Engineers,  vol.  xvii.  p.  338,  and 
credited  to  Prof.  L.  M.  Norton,  as  follows: 

CAUSES   OF   INCRUSTATION. 

1.  Deposition  of  suspended  matter. 

2.  Deposition  of  salts  from  concentration. 

3.  Deposition  of  carbonates  of  lime  and  magnesia  by  boiling  off 
carbonic  acid,  which  holds  them  in  solution. 

4.  Deposition  of  sulphates  of  lime,  because  sulphate  of  lime  is  sol- 
uble in  cold  water,  less  soluble  in  hot  water,  insoluble  above  270°  F. 

5.  Deposit  of  magnesia,  because  certain  magnesium  salts  decompose 
at  high  temperatures. 

6.  Deposition  of  lime-soap,  iron-soap,  etc.,  formed  by  saponifica- 
tion  of  grease. 

METHODS  OF  PREVENTING  INCRUSTATION. 

1.  Filtration. 

2.  Blowing  off. 

3.  Use  of  internal  collecting  apparatus,  or  devices  for  directing 
the  circulation. 

4.  Heating  feed -water. 

5.  Chemical  or  other  treatment  of  wafer  in  boiler. 

6.  Introduction  of  zinc  in  boiler. 

7.  Chemical  treatment  of  water  outside  of  boiler. 

Troublesome  Substance.  Trouble.  Remedy  or  Palliation.  - 

Sediment,  mud,  clay,  etc.  Incrustation.      Filtration;  blowing  off. 

Readily  soluble  salts.  Incrustation.      Blowing  off. 

Bicarbonates    of    lime,  mag-  )  Tnr.ril(jtjlt:nn    j  Heating  feed;  addition  of  caustic 
nesia,  and  iron.  \  '   \      soda,  lime,  etc. 

*  The  author  has  taken  the  lib<>rty  of  altering  tin's  table  somewhat  from  the  original. 


322  STEAM-BOILER  ECONOMY. 

Troublesome  Substance.  Trouble.  Remedy  or  Palliation. 

Su,puate  of  lim.  Incrustation,  j  ^Z  &S£T    ° 

Chloride  of  magnesium.  Corrosion.        Addition  of  carbonate  of  soda,  etc. 

°  amount.^    S°da  in  large  |     Priming.          Addition  of  barium  chloride,  etc. 
Acid  (in  mine-water).  Corrosion.        Alkali 

Dissolved  carbonic  acid  and  )      -,          .          j  Feed  milk  of  lime  to  the  boiler,  to 

oxygen.  f  \      form  a  thin  internal  coating. 

Grease       (from       condensed  (   Corrosion  or  ^ 

water).  (  incrustation.    |  Different  cases    require    different 

{Priming,      V     remedies.     Consult  a  specialist 
corrosion,  or  |      on  the  subject, 
incrustation.  J    • 

The  subject  of  the  scientific  treatment  of  bad  feed-waters  is  a 
large  and  complex  one,  and  the  practical  application  of  the  proper 
methods  is  rather  recent  in  this  country.  Those  who  are  further  in- 
terested in  this  matter  should  consult  the  paper  of  Messrs.  Hunt  and 
Clapp,  from  which  the  above  summary  is  taken,  and  also  Mr.  Albert 
A.  Gary's  paper  on  Corrosion  and  Scale  from  Feed-waters,  in  the  En- 
gineering Magazine  for  March,  April,  May,  and  June,  1897.  Accounts 
of  the  use  of  petroleum  for  preventing  incrustation  will  be  found  in 
Trans.  Am.  Soc.  M.  E.,  vol.  ix.  and  xi.,  a  statement  of  the  method  of 
purification  used  by  the  Solvay  Process  Company,  Syracuse,  N.  Y.,  in 
vol.  xiii.  p.  255,  and  a  description  of  the  method  used  on  the  line  of 
the  Southern  Pacific  Eailway  in  a  paper  by  Mr.  Howard  Stillman,  in 
vol.  xix.  p.  415. 

The  Use  of  Boiler  Compounds.* — To  the  majority  of  steam-users, 
anything  that  is  put  into  a  boiler  to  lessen  troubles  due  to  the  forma' 
tion  of  scale,  is  a  "  boiler  compound,"  and  the  fact  that  these  various 
so-called  compounds  act  differently  in  their  endeavor  to  accomplish 
their  purpose  is  not  generally  understood.  Such  nostrums  may  be  di- 
vided into  three  classes: 

First — Those  attacking  the  scale-producing  material  chemically. 
These  act  as  reagents  and  combine  with  the  matter  precipitated  from 
the  feed-water,  forming  a  third  substance  different  from  either  the 
original  precipitated  solids  or  the  "  reagent,"  the  theory  being  that  the 
new  substance  will  not  form  into  a  hard,  resisting  scale,  and  therefore 
can  be  more  easily  removed  by  blowing  off  or  by  the  cleaning-tools 
used  after  the  boiler  is  opened. 

Second — Those  acting  mechanically  upon  the  precipitated  crys- 
tals of  scale-making  matter  soon  after  they  are  formed.  Such  "com- 
pounds" are  of  a  glutinous,  starchy  or  oily  nature,  and  become  at- 
tached to  the  surface  of  the  newly  formed  crystals  (precipitated  from 

*  From  an  article  by  Albert  A.  Gary  in  American  Machinist,  Dec.  7,  1899. 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     323 

the  water)  surrounding  them,  as  the  skin  does  an  orange;  and  when 
these  crystals  fall  together  they  are  thus  robbed  of  their  cement-like 
action,  which  frequently  occurs  when  they  are  allowed  to  come  in  im- 
mediate contact. 

Third — Those  acting  both  mechanically  (as  just  described)  and  also 
as  a  solvent,  the  latter  action  partially  dissolving  scale  already  formed, 
and  by  this  "  rotting  "  effect  (as  it  is  often  called)  preparing  the  scale 
for  easy  removal. 

The  "  compounds  "  under  the  first  division  (which  act  chemically 
upon  the  scale-forming  matter)  also  frequently  accomplish  this  same 
rotting  effect  upon  scale  formed  previous  to  their  use.  Still  other  di- 
visions or  sub-divisions  might  possibly  be  made,  but  the  above  will 
suffice  for  a  good  general  idea  of  the  subject. 

Taking  up  our  first  division  of  this  subject,  we  find  that  the  prin- 
cipal ingredients  used  in  such  "  compounds  "  are  soda  ash  (or  carbon- 
ate of  soda)  and  tannin  matters,  while  we  sometimes  find  caustic  soda, 
sal  soda,  acetic  acid,  and  numerous  other  active  agents  which  are  gen- 
erally less  efficient  in  their  action  on  the  scale-forming  matter  and 
more  harmful  to  the  boiler  and  its  fittings. 

In  order  to  disguise  these  very  cheap  chemicals  and  help  the  "  com- 
pound "  vender  get  big  prices  for  his  powder  or  liquid,  whichever 
it  may  be,  there  are  often  added  other  substances  which  generally 
render  the  active  agents  less  efficient,  and  they  frequently  fall  un- 
changed to  the  bottom  of  the  boiler  with  the  scale,  thus  increasing 
the  deposit  and  aggravating  the  trouble. 

Such  added  substances  include  clay,  chalk,  sand,  etc.,  and  some- 
times coloring  matter  is  used  to  disguise  the  original  chemicals,  such 
as  tooacco-juice,  iron  scraps,  lampblack,  spent  tan,  etc. 

The  principal  scale-making  impurities  precipitated  in  boilers  are 
carbonate  of  lime  (CaC03),  carbonate  of  magnesium  (MgC03),  sul- 
phate of  lirn^  (OaSOJ  and  sulphate  of  magnesium  (MgS04),  and  al- 
though there  are  generally  other  precipitates,  notice  of  these  alone 
will  be  sufficient  for  the  present  consideration. 

The  chemical  action  taking  place  when  some  of  the  above-named 
active  agents  are  used  may  be  traced  as  follows  : 

Soda  ash  is  a  dry  impure  carbonate  of  soda,  from  which  the  pure 
alkali  is  afterwards  made. 

The  carbonate  of  soda  (Na2C03)  is  used  to  act  upon  the  sulphate 
of  lime  and  magnesia,  as  shown  in  the  following  chemical  formulae : 

f  v    Sulphate         ,     Carbonate     .  Carbonate         -,     Sulphate 

W    of  time     and      of  Soda        form      of  Lime      and     of  Soda. 
CaS04       +        Na.00,  CaCO,         +        Na2S04 

m    Sulphate  of        ,  Carbonate  .          Carbonate  of        -,  Sulphate 
W    Magnesium   and     of  Soda     form       Magnesia      and    of  Soda 
MgS04        +       Na2C03       =  MgCO,        +      Na,S04 

Both  the  carbonate  of  lime  and  carbonate  of  magnesia  are  held  in 
solution  through  the  presence  of  carbonic  acid  gas  dissolved  in  the 


324  STEAM-BOILER  ECONOMY. 

water,  which  unites  with  them  and  changes  the  mono-carbonates  inta 
bicarbonates  (which  are  only  known  to  exist  in  solution),  as  shown 
thus: 


CaOCOa     +       CO,      +      H90     =  CaO(CO,)aH30  =  CaHa(C08)a 

In  a  similar  manner  the  bicarbonate  of  magnesium  is  formed 
from  the  monocarbonate  thus  : 

Carbonate  of         ,      Carbonic         ,   Wat^r   form       Bicarbonate          Generally 
Magnesium      and          Acid        and  l     of  Magnesium,       Expressed 

MgOC03          +  CO2          -f      H2O       =      MgO(CO2)2H2O  =  MgH2(CO3)2 

The  monocarbonates  (or  single  carbonates)  of  lime  and  magnesia 
are  but  slightly  soluble  in  water,  whereas  the  bicarbonates  (or  double 
.carbonates)  are  very  soluble  in  cold  water,  and  this  fact  will  account 
for  the  presence  of  the  large  quantities  of  lime  and  magnesia  in  boiler 
waters  as  carbonates. 

When  waters  containing  the  bicarbonates  are  heated,  the  rise  in 
temperature  drives  off  the  extra  carbonic  acid  gas  and  leaves  behind 
the  practically  insoluble  monocarbonates,  which  are  precipitated. 

When  a  temperature  of  180°  Fahr.  is  reached,  a  considerable  per- 
centage of  the  bicarbonates  is  precipitated  (as  insoluble  monocar- 
bonates), and  at  290°  Fahr.  (a  temperature  corresponding  to  43  Ibs, 
gauge-pressure)  the  precipitation  is  nearly  completed,  after  a  thor- 
ough boiling. 

Scale  formed  from  the  monocarbonate  of  lime  is  seldom  very 
troublesome,  if  not  allowed  to  accumulate  in  too  large  a  quantity,  nor 
allowed  to  remain  in  the  boiler  for  a  long  time;  while  the  precipi- 
tated monocarbonate  of  magnesia  gives  slightly  more  trouble,  due 
to  the  fact  that  it  seldom  is  found  in  scale  as  a  monocarbonate.  All 
the  contained  carbonic  acid  (009)  is  generally  lost  from  the  bicar- 
bonate of  magnesia  (MgO(COa)aH,0)  by  the  time  it  forms  a  crust, 
leaving  behind  the  hydrate  of  magnesia  (MgO  -f-  HaO  =  MgOJIJ,. 
which  acts  as  a  cement  and  binds  closely  together  (though  not  very 
strongly)  whatever  precipitated  matter  it  may  come  in  contact  with. 

This  hydrate  of  magnesia  is  very  fine  and  light  when  precipitated 
and  requires  a  comparatively  long  time  to  settle. 

The  sulphates  of  lime  and  magnesia  are  very  soluble,  dissolving  in 
water  direct,  without  requiring  the  presence  of  carbonic  acid  or  any 
other  foreign  agent. 

The  amount  of  sulphate  of  lime  which  can  be  dissolved  in  one 
United  States  gallon  of  water  at  different  temperatures  may  be  ap- 
preciated by  examining  the  following  table  : 

At  32°  Fahr.,  120  grains  per  gallon. 
At  95°  Fahr.,  148  grains  per  gallon. 
At  212°  Fahr.,  127  grains  per  gallon. 
At  250°  Fahr.,  9  grains  per  gallon. 
At  from  260°  to  302°  Fahr.,  it  is  practically  insoluble. 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     325 

This  latter  temperature  (302°)  corresponds  to  55  Ibs.  gauge-pres- 
sure, and,  therefore,  when  water  is  thoroughly  boiled  at  this  tempera- 
ture, practically  all  of  the  sulphates  will  be  precipitated.  The  crys- 
tals of  sulphate  of  lime  will  be  found  to  be  long  and  needle-like,  and 
also  very  heavy  and  possessing  cement-like  qualities,  so  they  fall 
rapidly,  and,  mixing  with  the  precipitated  carbonates,  they  bind  them 
together  into  a  hard,  resisting  mass,  difficult  to  remove  with  even 
hammer  and  chisel,  if  they  form  a  considerable  proportion  of  the 
scale. 

It  is  here  where  the  active  agent  in  the  compound  is  supposed  to 
take  effect,  and  by  referring  to  the  reaction  given  above — in  the 
formulae  (a)  and  (b) — when  the  carbonate  of  soda  is  used,  it  will  be 
seen  that  the  sulphates  of  lime  and  magnesia  are  changed  into  car- 
bonates, which  are  precipitated  and  form  a  scale  varying  from  a  more 
or  less  porous,  friable  crust  to  a  "mush  "  or  mud.  The  sulphate  of 
soda,  which  is  also  formed  by  this  reaction,  is  extremely  soluble,  re- 
maining in  solution  at  nearly  all  boiler  temperatures  and  forming  no 
scale,  unless  allowed  to  concentrate,  and  this  is  prevented  by  "  blow- 
ing off  "  occasionally. 

The  tannin  matters,  referred  to  above,  are  obtained  from  various 
vegetable  sources  containing  tannic  acid,  such  as  certain  kinds  of 
sumach,  gallnuts,  catechu  (or  cutch)  bark,  etc.  Tannin  is  generally 
combined  with  soda  to  form  the  tannate  of  soda  for  use  with  boiler 
waters  to  keep  the  deposit  soft  or  in  suspension.  Its  action  is  sup- 
posed to  be  as  follows : 

The  tannate  of  soda  decomposes  the  carbonates  of  lime  and  mag- 
nesia as  they  enter  the  boiler,  and  tannates  of  lime  and  magnesia  are 
precipitated  in  a  light,  flocculent,  amorphous  form  and  are  long  kept 
in  suspension  by  the  circulating  currents  of  water,  until  they  finally 
are  deposited  in  a  loose,  mushy  mass  in  that  part  of  the  boiler  where 
the  circulating  currents  are  the  weakest,  or  possibly  in  the  mud-drum. 

When  the  above  reaction  takes  place  the  carbonate  of  soda  is 
formed,  which  reacts  with  any  sulphates  that  may  be  present,  as  has  al- 
ready been  described. 

The  use  of  tannic  acid  in  the  boiler  cannot  be  recommended  un- 
reservedly, as  it  will  attack  the  iron  as  well  as  the  carbonates  (al- 
though, of  course,  more  slowly),  and  anything  that  will  corrode  the 
boiler  itself  certainly  cannot  be  desirable.  To  test  this,  any  one  can 
obtain  a  few  cents"  worth  of  tannic  acid  from  the  druggist,  and  by 
dissolving  the  crystals  in  a  glass  of  water  and  adding  some  iron  fil- 
ings a  very  fair  quality  of  ink  can  be  made,  due  to  the  action  of  this 
acid  on  the  iron. 

In  practice,  the  reaction  of  caustic  soda  (Naa02H2)  with  the  sul- 
phates seems  to  be  more  active  than  when  the  carbonate  of  soda  is 
used,  the  probable  reaction  being  as  shown  thus: 

Sulphate  ,  Carbonic  -,  Caustic  -_  Caustic  -,  Carbonic  ,  Sulphate 
of  Lime  and  Acid  and  Soda  form  Lime  and  Acid  and  of  Soda. 
CaS04  +  C02  -f  2NaOH  =  CaHa02  +  CO,  +  Na2SO4 

The  carbonic  acid  used  in  this  formula  results  from  the  precipita- 


326  STEAM-BOILER  ECONOMY. 

tion  of  the  monocarbonates  from  the  bicarbonates,  as  has  been   ex- 
plained. 

The  secondary  reaction  from  the  result  just  arrived  at  is  as  follows: 

C^tic    Rnd    Carbonic    ^    C^bonate    and    ^ 
CaHa02      +          C02  CaOCO,        +       H,0 

The  use  of  caustic  soda  may  be  considered  less  desirable  than  the 
use  of  the  carbonate  of  soda  for  several  reasons. 

In  the  first  place  this  present  in  excess  will  cause  violent  foaming 
in  the  boiler,  and  with  this  foam  often  the  light  precipitated  matter 
in  the  boiler  will  be  carried  along  steam-pipes  into  valve-seats,  gauge- 
glasses,  etc.  It  will  also  attack  and  cause  corrosion  of  the  brass  fit- 
tings, and  it  is  also  dangerous  to  handle,  owing  to  its  caustic  qualities, 
burning  the  flesh  painfully  wherever  it  comes  in  contact. 

An  excess  of  carbonate  of  soda  may  also  cause  foaming  in  the 
boiler,  but  not  as  violent  as  when  caustic  soda  is  used. 

Sal  ammoniac  (ammonium  chloride,  NH3HC1)  is  most  undesirable 
for  use  in  a  boiler,  due  to  the  liberation  of  hydrochloric  acid  (HC1) 
following  its  introduction  into  the  boiler.  This  acid  leaves  the  boiler 
in  a  vaporous  form,  with  the  steam,  corroding  the  boiler,  piping,  and 
nearly  everything  it  comes  in  contact  with. 

There  are  other  "  compounds"  falling  under  this  classification,  of 
known  chemical  composition,  which  are  more  satisfactory  than  those 
named  above,  such  as  bisodium  phosphate  and  tri sodium  phosphate, 
the  latter  being  obtainable  in  both  a  hydrous  and  anhydrous  state.  The 
latter  is  less  bulky  and  its  reaction  with  the  sulphate  of  lime  is  shown 
by  the  following  formula : 

2  Parts  3  Parts 

Trisodium  and    Sulphate  form  Phosphate  ,              3  Parts 

Phosphate  of  Lime                of  Lime  Sulphate  of  Soda. 

2Na3P04  +       3CaS04      =      Ca3(P04),  +             3Na,S04 

The  phosphate  of  lime,  after  this  reaction,  falls,  forming  a  slushy 
mud,  making  at  the  most  a  very  weak  crust,  while  the  sulphate  of  soda 
remains  in  solution,  as  previously  described. 

The  fluoride  of  sodium  is  another  "  compound  "  of  known  composi- 
tion, which  has  also  proved  satisfactory,  especially  when  much  sul- 
phate of  magnesia  is  present;  its  reaction  with  the  sulphate  of  lime 
being  as  follows: 

2  Parts  of  -,    Sulphate    .  Fluoride        -,    Sulphate 

Fluoride  of  Sodium     ana     of  Lime  of  Lime    and    of  Soda 

2(NaF)  +        CaS04         =          CaF2         +     NaaS04 

The  fluoride  of  lime  precipitated  in  the  boiler  behaves  much  like 
the  phosphate  of  lime  just  described,  while  the  remaining  sulphate  of 
soda  is  found  in  solution,  as  stated  above. 

The  second  division  of  compounds  includes  a  class  of  materials 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     327 

which  are  gradually  falling  into  disuse,  due  to  their  proved  undesira- 
bility.  They  thicken  and  foul  the  water  in  the  boiler  and  coat  its  sur- 
faces with  non-conducting  material,  and  occasionally  the  precipitated 
scale-making  matter,  along  with  this  class  of  compound,  will  obstruct 
the  passage  of  heat  through  the  boiler-plates,  so  as  to  cause  bagging  and 
burning. 

In  this  class  we  find  slippery  elm,  ground  bones,  horns  and  hoofs, 
potatoes,  dextrine,  and  starch,  animal  fats  and  animal  or  vegetable 
table  oils. 

As  rapidly  as  the  scale-forming  crystals  are  precipitated  from  the 
feed-water,  they  fall  into  this  sticky  fluid  and  become  coated  with  its 
filth,  and  they  finally  fall  to  the  place  of  deposit,  where  they  remain  in 
a  mushy,  separated  state  until  the  organic  matter  chances  to  be  burned 
out,  when  they  will  form  into  a  loose,  friable  scale. 

A  surface  blow-off  or  skimming  device  is  most  essential  to  reduce 
the  evil,  when  this  class  of  compound  is  used,  and  the  botton  blow-off 
cock  should  also  be  opened  very  frequently. 

The  principal  substances  used  for  the  third  class  of  compounds  are 
petroleum  and  kerosene. 

Petroleum  oil  has  much  more  of  the  enveloping  quality  described 
under  the  last  (or  third)  classification  than  the  kerosene.  Besides  pro- 
ducing this  effect  on  the  scale-matter,  both  have  an  active  rotting 
effect  on  the  scale  already  formed,  the  kerosene  in  this  case  being 
superior  to  the  petroleum. 

Crude  oil  should  never  be  used,  but  a  carefully  refined  oil,  which 
has  been  deprived  of  its  tar  or  wax,  should  be  selected  for  this  pur- 
pose, as  these  cause  the  formation  of  a  tough,  impervious  scale  pro- 
ductive of  bagged  sheets  and  collapsed  flues.  Petroleum  or  kerosene 
should  be  fed  to  the  boiler  with  the  feed-water,  drop  by  drop,  through 
a  sight-feed  apparatus  similar  to  those  used  to  feed  oil  to  the  cylinders 
of  engines.  IJnder  no  consideration  should  large  amounts  of  these 
oils  be  fed  to  a  boiler  at  one  time,  as  it  must  be  remembered  that  the 
more  volatile  portion  of  the  petroleum  will  be  quickly  distilled  off  in 
the  hot  boiler,  leaving  the  least  efficient  portion  behind,  while  thw 
more  volatile  kerosene  will  be  vaporized  very  quickly,  before  it  has 
time  to  thoroughly  mix  with  the  water. 

Where  hard  scale  has  formed  in  a  boiler,  it  is  most  effectually 
treated  by  giving  it  a  coat  of  petroleum  or  kerosene,  to  partially  dis- 
solve or  rot  it.  This  may  be  applied  with  a  brush  or  squirted  on,  but 
an  easier  method  of  application  is  to  first  fill  the  boiler  with  water 
above  the  line  of  scale-deposit  and  then  pour  the  oil  on  the  surface  of 
this  water  and  let  the  water  gradually  run  out  of  the  bottom  of  the 
boiler,  thus  leaving  the  oil  behind  clinging  to  the  whole  interior 
surface.* 

*  An  effective  method  of  cleaning»a  boiler  which  has  become  heavily  coated 
with  hard  sulphate  of  lime  scale,  is  to  put  in  it  a  large  quantity  of  caustic  soda, 
say  50  Ibs.  for  a  large  boiler,  and  boil  it  at  atmospheric  pressure,  the  safety-valve 
being  opened,  for  several  hours.  This  converts  the  hard  scale  into  a  soft  sub- 
stance which  may  be  removed  by  a  scraper,  followed  by  thorough  washing  with 
cold  water.— W.  K. 


328  STEAM-BOILER  ECONOMY. 

As  stated  above,  kerosene  is  the  most  effective  in  destroying  the 
tenacity  or  coherence  of  this  deposited  scale,  but  this  method  of  using 
either  oil  is  not  without  attending  danger,  on  account  of  the  explo- 
siveness  of  the  vapor  given  off  ;  so  great  care  must  be  taken  to  have 
no  lights  in  the  vicinity  of  the  boiler  under  such  treatment,  as  men 
have  been  seriously  injured  by  this  lack  of  prudence. 

The  treatment  of  feed-waters  inside  of  the  boiler  has  been  a  prac- 
tice of  many  years'  standing,  but  in  the  light  of  recent  progress  is  not 
to  be  commended.  A  boiler  certainly  has  all  that  it  can  reasonably  be 
expected  to  do  when  it  is  generating  steam  without  being  called  upon 
to  perform  the  functions  of  a  chemical  laboratory. 

The  external  method  of  treating  feed-water,  chemically  or  me- 
chanically, is  being  adopted  by  many  progressive  plants  in  this  coun- 
try; but  in  this,  Americans  are  far  behind  the  English,  French,  Ger- 
mans, Belgians,  and  Austrians,  in  whose  countries  the  external  treat- 
ment has  been  largely  and  most  successfully  practised  for  many  years. 

There  are,  of  course,  plants  where  the  internal  treatment  of  feed- 
water  is  an  enforced  necessity,  owing  to  surrounding  conditions  or  lack 
of  funds  necessary  to  install  apparatus  for  external  treatment,  but  as 
such  apparatus  has  invariably  proved  to  be  an  excellent  investment,  it 
should  receive  careful  consideration  from  all  steam-users. 

External  Corrosion  is  a  frequent  cause  of  dangerous  weakening  of 
a  steam-boiler.  It  is  most  commonly  due  to  dampness,  and  is  there- 
fore more  liable  to  take  place  when  a  boiler  is  out  of  service  and  cold 
than  when  it  is  in  use  and  constantly  kept  hot.  The  most  active 
agent  of  corrosion  is  sulphurous  acid  gas,  produced  from  the  sulphur 
in  the  coal,  which  is  converted  into  sulphuric  acid  in  the  presence  of 
moisture  in  the  cold.  Mud-drums  and  other  parts  of  a  boiler  which 
are  farthest  removed  from  the  fire,  and  on  which  there  is  apt  to  be 
an  accumulation  of  damp  soot  or  dirt,  are  especially  subject  to 
external  corrosion.  The  precautions  to  be  taken  to  prevent  this  kind 
of  corrosion  are  to  have  the  boiler  frequently  inspected  and  to  keep 
it  clean,  dry,  and  hot. 

The  Life  of  a  Steam-boiler. — What  is  known  as  the  "  life "  of  a 
boiler  generally  depends  upon  the  amount  of  corrosion  to  which  it  is 
subjected.  With  good  feed-water  which  will  neither  corrode  the 
metal  nor  cause  the  deposit  of  a  dangerous  scale,  and  with  care  to 
keep  the  outside  surface  perfectly  dry,  a  life  of  forty  years  for  a  boiler 
is  not  uncommon.  With  slow  corrosion  its  life  may  be  reduced  to 
five  years  or  less,  with  the  additional  inconvenience  that  the  pressure 
of  steam  which  may  be  safely  carried  is  continually  being  reduced 
during  its  life. 

Besides  corrosion  other  causes  tending  to  shorten  the  life  of  a 


BOILER  TROUBLES  AND  BOILER-USERS'   COMPLAINTS.     329 

boiler  are:  (1)  Tendency  to  accumulation  of  scale,  mud,  or  grease  on 
the  plates  over  or  near  to  the  fire,  causing  "  bagging "  of  plates, 
leakage  of  seams,  and  sometimes  explosions.  (2)  Overheating  of 
riveted  seams  where  they  overlap,  especially  when  they  are  covered 
with  scale.  (3)  Hidden  defects,  due  to  strains  or  other  causes,  such 
as  those  described  below. 

Defects  Discovered  by  Inspection. — The  Locomotive,  published  by 
the  Hartford  Steam-boiler  Inspection  and  Insurance  Co.,  in  its  issue 
of  February,  1900,  gives  the  following  statement  showing  the  number 
and  kind  of  defects  discovered  by  the  inspectors  of  that  company 
during  the  year  1899 : 

During  the  year  1899  our  inspectors  made  112,464  visits  of 
inspection,  examined  221,706  boilers,  inspected  85,804  boilers  both 
internally  and  externally,  subjected  9,371  to  hydrostatic  pressure,  and 
found  779  unsafe  for  further  use.  The  whole  number  of  defects 
reported  was  157,804,  of  which  12,800  were  considered  dangerous. 
A  classification  of  the  defects  is  given  below : 

SUMMARY,    BY   DEFECTS,     FOE,  THE   YEAR    1899. 

Nature  of  Defects.  Whole  Number.  Dangerous. 

Cases  of  deposit  of  sediment 11,974  740 

Cases  of  incrustation  and  scale  29,0-">2  817 

Cases  of  internal  grooving 1.602  140 

Cases  of  internal  corrosion 8,489  424 

Cases  of  external  corrosion 7,018  482 

Defective  braces  and  stays  2, 166  809 

Settings  defective 3,990  304 

Furnaces  out  of  shape 4,820  238 

Fractured  plates 3,622  512 

Burned  plates 3,361  386 

Blistered  plates r...  1,952  74 

Defective  rivets 24,550  1,358 

Defective  beads 1. 165  206 

Leakage  around  tubes 31,583  3,403 

Leakage  at  seams 4,783  31 3 

Water-gauges  defective 3,253  626 

Blow-outs  defective 2,059  581 

Cases  of  deficiency  of  water 188  80 

Safety-valves  overloaded 973  433 

Safety-valves  defective    1 .028  275 

Pressure-gauges  defective 4.947  394 

Boilers  without  pressure-gauges 203  203 

Unclassified  defects 5,027  2 

Total 157,804        12,800 

Explosions  Caused  by  Hidden  Defects. — It  is  the  common  opinion 
that  explosions  are  due  to  carelessness  of  handling  by  the  firemen,  or 
to  negligence  of  inspectors  in  not  discovering  defects,  but  occasionally 


330  STEAM-BOILER  ECONOMY. 

an  explosion  takes  place  which  is  not  due  to  either  of  these  causes. 
On   February  27,  1897,  a  disastrous   explosion   took   place   at   the 
Acushnet  Mills,  New  Bed- 
ford,   Mass.,   wrecking    a 
portion  of   the  mills  and 
killing  and  injuring  sev- 
eral persons.     The  boiler 
that    exploded   was    built  FlG>  m_ A  HIDDEN  CRACK. 

in     1890.       Examination 

showed    that    the    break  X^V  /\ 

was  almost  identical  with  ^HH^— V    .'/  J     y   ' 

that   of   the  explosion  of 

,    .,  -1       T        i  FIG.  109. — SECTION  OP  SEAM. 

a   boiler   at   the    Langley 

factory,  Fall  Eiver,  Mass.,  in  June,  1895,  which  boiler  was  made  by 
the  same  builders  that  made  the  boiler  in  New  Bedford.  The  boiler 
parted  in  a  horizontal  seam  of  the  middle  sheet,  close  to  the  rivet- 
holes,  and  under  the  lap,  and  the  fault  was  owing  to  a  crack  in  the 
plates  under  the  outer  edge  of  the  rivet-heads,  as  shown  in  the 
accompanying  cuts,  Figs.  108  and  109.  The  Locomotive  speaking  of 
this  class  of  fractures  says : 

Most  of  the  fractures  of  the  plate  are  undoubtedly  due  to  the 
bending  of  the  plates  in  the  rolls.  From  30  to  40  per  cent  of  the 
sectional  area  of  the  plate  is  removed  along  the  line  of  the  joint  by 
punching  or  drilling  the  rivet-holes;  and  when  the  part  that  is  thus 
weakened  is  passing  through  the  rolls,  the  curvature  of  the  plates  at 
this  point  is  sensibly  increased.  When  the  plates  thus  affected  are 
brought  into  position  for  riveting  they  will  not  lie  closely,  but  have 
to  be  knocked  together  with  a  sledge,  or  forced  together  hydro- 
statically,  before  the  rivets  can  be  driven.  This  means  that  there  is 
a  severe  local  strain  left  in  the  plates,  the  effects  of  which  are  likely 
to  become  visible  at  some  time  in  the  subsequent  history  of  the 
'boiler.  When  the  joint  has  been  riveted  up,  the  parts  of  the  plate 
that  lie  under  the  heads  of  the  rivets  are  held  together  so  firmly  that 
the  yielding  action  that  occurs  in  every  boiler,  as  the  pressure  and 
temperature  vary,  will  not  be  felt  at  this  point,  but  will  be  transferred 
to  a  line  lying  at,  or  just  beyond,  the  edge  of  the  rivet-heads.  In 
the  course  of  time  these  slight  changes  of  form,  when  combined  with 
the  stress  already  existing  along  this  line  from  the  cause  just 
described,  are  likely  to  develop  a  crack  starting  from  the  inside 
surface  of  the  outer  plate,  at  a  place  completely  hidden  from 
view,  and  extending  insidiously  outward,  until  the  final  rupture 
of  the  plate  is  accomplished,  and  the  boiler  gives  way  in  a  violent 
explosion. 


BOILER  TROUBLES  AND  BOILER-USERS*    COMPLAINTS.    331 

Here  is  the  record  of  an  explosion  due  to  a  cause  that  had  been 
concealed  for  seven  years,  and  which  cause  was  so  hidden  that  it  could 
not  be  found  by  either  external  or  internal  inspection. 

It  may  be  said  that  this  accident  and  that  at  the  Langley  mill,  in 
1895,  would  not  have  happened  if  the  boilers  had  been  properly  made, 

and  if  the  riveted  joint  had  been  of  the 
form  shown  in  Fig.  110;  but  it  must  be 
remembered  that   the   horizontal  tubular 
FIG.  110.— BUTT  AND  STRAP   boiler  is  favored  chiefly  on  account  of  its 
NT*  low  first  cost,  and  low  cost  is  generally  not 

compatible  with  the  highest  excellence  of  material  and  workmanship. 
If  a  cheap  form  of  boiler  is  selected  and  the  contract  given  to  the 
lowest  bidder,  it  is  only  to  be  expected  that  cheap  material,  cheap 
workmanship,  and  unskilled  designers  are  likely  to  be  employed  in  its 
construction. 

The  water-  and  steam-drum  of  a  water-tube  boiler  being  much 
smaller  than  the  shell  of  a  fire-tube  boiler,  and  costing  a  much  smaller 
percentage  of  its  total  cost,  there  is  not  the  same  temptation  to  make 
the  drum  cheap  that  there  is  with  the  shell  boiler. 


CHAPTEE  XIV. 
EVAPORATION  TESTS  OF  STEAM-BOILERS. 

Object  of  an  Evaporation  Test. — The  principal  object  of  an 
evaporation  test  of  a  steam-boiler  is  to  find  out  how  many  pounds  of 
water  it  evaporates  under  a  certain  set  of  conditions  in  a  given  time, 
and  how  many  pounds  of  coal  are  required  to  effect  this  evaporation. 
The  test  may  be  made  for  one  or  more  of  several  purposes,  viz : 

1.  To  determine  whether  or  not  the  stipulations  of  a  contract  be- 
tween the  seller  and  the  buyer  of  a  boiler  (or  of  an  appendage  to  the 
boiler,  such  as  a  furnace)  have  been  performed. 

2.  To  determine  the  relative  economy  of  different  kinds  of  fuel, 
of  different  kinds  of  furnace,  or  of  different  methods  of  driving. 

3.  To  determine  whether  or  not  the  boilers,  as  ordinarily  run  under 
the  every-day  conditions  of  the  plant,  are  operated  as  economically  as 
they  should  be. 

4.  To  determine,  in  case  the  boilers  either  fail  to  furnish  easily 
the  quantity  of  steam  desired,  or  else  furnish  it  at  what  is  supposed  to 
be  an  excessive  cost  for  fuel,  whether  any  additional  boilers  are  needed 
or  whether  some  change  in  the  conditions  of  running  is  a  sufficient 
remedy  for  the  difficulty. 

For  the  first  of  the  above-named  purposes,  it  is  necessary  that  the 
test  should  be  made  with  every  precaution  to  insure  accuracy,  such  as 
those  described  in  the  Code  of  the  Committee  of  the  American  Society 
of  Mechanical  Engineers,  which  is  given  below.  Experts  in  boiler- 
testing  should  be  employed,  and  the  water  fed  to  the  boiler  should  be 
weighed,  or  measured  in  calibrated  tanks,  and  not  by  a  water-meter, 
which  is  apt  not  only  to  have  an  error  at  its  average  rate  of  running, 
but  also  an  error  which  varies  with  every  change  in  the  rate.  For  the 
other  three  purposes,  however,  water-meters,  if  calibrated  before  and 
after  the  test  by  means  of  running  water  through  them,  at  the  average 
rate  and  pressure  used  in  the  test,  into  a  tank  set  on  a  platform  scale, 

332 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  333 

are  sufficiently  accurate,  and  the  regular  engineering  force  of  the  estab- 
lishment should  be  capable  of  making  the  test. 

In  large  plants,  in  which  the  yearly  cost  of  coal  amounts  to  some 
thousands  of  dollars,  there  are  apt  to  be  wastes  of  fuel,  amounting  to 
as  much  as  10  or  20  per  cent  of  the  total  consumption,  which  are 
unsuspected  until  they  are  discovered  by  a  series  of  tests.  When 
several  boilers  discharge  their  gases  into  the  same  flue  leading  to  the 
chimney,  unless  the  draft  conditions  at  each  boiler  are  carefully  equal- 
ized, one  or  more  of  the  boilers  is  likely  to  be  running  under  unfavor- 
able draft  conditions.  If  the  boilers  are  of  different  types  or  different 
proportions  of  grate  and  heating  surface,  the  draft  and  the  method  of 
firing  which  are  best  for  one  boiler  may  not  be  best  for  another.  For 
these  reasons  it  is  important  in  designing  and  constructing  a  large 
boiler  plant  to  arrange  the  feed-pipes  so  that  a  meter  may  at  any  time 
be  placed  in  the  feed-pipe  of  any  one  of  the  boilers,  in  order  that  a  test 
of  24  hours,  or  a  week,  if  desired,  may  easily  be  made.  It  is  an  easy 
matter  to  weigh  all  the  coal  used  by  the  boiler  during  the  test,  and  to 
keep  hourly  records  of  the  coal-  and  water-consumption,  the  steam 
pressure,  and  the  temperatures  of  the  feed-water  and  the  waste  gases. 

Besides  the  tests  of  each  boiler  in  a  plant,  which  ought  to  be  made 
occasionally,  say  every  two  or  three  years,  a  continuous  record  of  the 
performance  of  the  plant  may  be  made  by  having  a  large  meter  in  the 
main  feed-line,  noting  the  water-consumption  daily, weekly,  or  monthly, 
and  comparing  it  with  the  monthly  coal  bills.  In  electric  light  and 
power  stations  the  boiler-record  should  be  compared  with  the  record  of 
the  electric  current  given  by  the  volt  and  ampere  meters. 

Eor  all  important  tests,  where  the  greatest  accuracy  is  essential,  the 
provisions  of  the  Code,  which  is  given  below,  should  be  followed. 

EULES  FOR  CONDUCTING  BOILER  TRIALS.     CODE  OF  1899.* 

I.  Determine  at  the  outset  the  specific  object  of  the  proposed  trial, 
whether  it  be  to  ascertain  the  capacity  of  the  boiler,  its  efficiency  as  a 
steam-generator,   its  efficiency  and  its  defects   under  usual  working 
conditions,  the  economy  of  some  particular  kind  of  fuel,  or  the  effect 
of  changes  of  design,  proportion,  or  operation;  and  prepare  for  the 
trial  accordingly. 

II.  Examine   the   boiler,    both   outside  and  inside;  ascertain  the 
dimensions  of  grates,  heating  surfaces,  and  all  important  parts;  and 

*From  the  report  of  the  committee  of  the  Am  Soc.  M.  E.  on  the  revision  of 
the  Society  Code  of  1885,  relative  to  a  standard  method  of  conducting  steam- 
boiler  trials. 


334  STEAM-BOILER  ECONOMY. 

make  a  full  record,  describing  the  same,  and  illustrating  special  fea- 
tures by  sketches.  The  area  of  heating  surface  is  to  be  computed 
from  the  surfaces  of  shells,  tubes,  furnaces,  and  fire-boxes  in  contact 
with  the  fire  or  hot  gases.  The  outside  diameter  of  water-tubes  and 
the  inside  diameter  of  fire-tubes  are  to  be  used  in  the  computation. 
All  surfaces  below  the  mean  water-level  which  have  water  on  one  side 
and  products  of  combustion  on  the  other  are  to  be  considered  as  water- 
heating  surface,  and  all  surfaces  above  the  mean  water-level  which 
have  steam  on  one  side  and  products  of  combustion  on  the  other  are  to 
be  considered  as  superheating  surface. 

III.  Notice  the  general  condition  of  the  boiler  and  its  equipment, 
and  record  such  facts  in  relation  thereto  as  bear  upon  the  objects  in 
view. 

If  the  object  of  the  trial  is  to  ascertain  the  maximum  economy  or 
capacity  of  the  boiler  as  a  steam-generator,  the  boiler  and  all  its  ap- 
purtenances should  be  put  in  first-class  condition.  Clean  the  heating 
surface  inside  and  outside,  remove  clinkers  from  the  grates  and  from 
the  sides  of  the  furnace.  Eemove  all  dust,  soot,  and  ashes  from  the 
chambers,  smoke-connections,  and  flues.  Close  air-leaks  in  the  ma- 
sonry and  poorly  fitted  cleaning-doors.  See  that  the  damper  will 
open  wide  and  close  tight.  Test  for  air-leaks  by  firing  a  few  shovels 
of  smoky  fuel  and  immediately  closing  the  damper,  observing  the 
escape  of  smoke  through  the  crevices,  or  by  passing  the  flame  of  a 
candle  over  cracks  in  the  brickwork. 

IV.  Determine  the  character  of  the  coal  to  be  used.     For  tests  of 
the  efficiency  or  capacity  of   the  boiler  for  comparison  with  other 
boilers  the  coal  should,  if  possible,  be  of  some  kind  which  is  commer- 
cially regarded  as  a  standard.     For  New  England  and  that  portion  of 
the  country  east  of  the  Allegheny  Mountains,   good  anthracite  egg 
coal,   containing  not  over  10  per  cent  of  ash,  and  semi-bituminous 
Clearfield  (Pa.),  Cumberland   (Md.),  and  Pocahontas  (Va.)  coals  are 
thus  regarded.     West  of  the  Allegheny  Mountains,  Pocahontas  (Va.) 
and   New   River    (W.  Va.)  semi-bituminous,  and  Youghiogheny  or 
Pittsburg  bituminous   coals  are  recognized  as  standards.*     There  is 
no  special  grade  of  coal  mined  in  the  Western  States  which  is  widely 
recognized  as  of  superior  quality  or  considered  as  a  standard  coal  for 
boiler  testing.     Big  Muddy  lump,  an  Illinois  coal  mined  in  Jackson 
County,  111.,  is  suggested  as  being  of  sufficiently  high  grade  to  answer 
these  requirements  in  districts  where  it  is  more  conveniently  obtain- 
able than  the  other  coals  mentioned  above. 

For  tests  made  to  determine  the  performance  of  a  boiler  with  a 
particular  kind  of  coal,  such  as  may  be  specified  in  a  contract  for  the 
sale  of  a  boiler,  the  coal  used  should  not  be  higher  in  ash  and  in  moist- 
ure than  that  specified,  since  increase  in  ash  and  moisture  above  a 

*  These  coals  are  selected  because  they  are  about  the  only  coals  which  possess 
the  essentials  of  excellence  of  quality,  adaptability  to  various  kinds  of  furnaces, 
grates,  boilers,  and  methods  of  firing,  and  wide  distribution  and  general  accessi- 
bility in  the  markets. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  335 

stated  amount  is  apt  to  cause  a  falling  off  of  both  capacity  and  econ- 
omy in  greater  proportion  than  the  proportion  of  such  increase. 

V.  Establish  the  correctness  of  all  apparatus  used  in  the  test  for 
weighing  and  measuring.     These  are: 

1.  Scales  for  weighing  coal,  ashes,  and  water. 

2.  Tanks,  or  water-meters  for  measuring  water.     Water-meters, 
as  a  rule,  should  only  be  used  as  a  check  on  other  measurements. 
For  accurate  work,  the  water  should  be  weighed  or  measured  in  a 
tank. 

3.  Thermometers  and  pyrometers  for  taking  temperatures  of  air, 
stearn,  feed-water,  waste  gases,  etc. 

4.  Pressure-gauges,  draft-gauges,  etc. 

The  kind  and  location  of  the  various  pieces  of  testing  apparatus 
must  be  left  to  the  judgment  of  the  person  conducting  the  test, 
always  keeping  in  mind  the  main  object,  i.e.,  to  obtain  authentic  data. 

VI.  See  that  the  boiler  is  thoroughly  heated  before  the  trial  to  its 
usual  working  temperature.     If  the  boiler  is  new  and  of  a  form  pro- 
vided with  a  brick  setting,  it  should  be  in  regular  use  at  least  a  week 
before  the  trial,  so  as  to  dry  and  heat  the  walls.     If  it  has  been  laid 
off  and  become  cold,  it  should  be  worked  before  the  trial  until  the 
walls  are  well  heated. 

VII.  The  boiler  and  connections  should  be  proved  to  be  free  from 
leaks  before  beginning  a  test,  and  all  water-connections,  including 
blow  and  extra  feed-pipes,  should  be  disconnected,  stopped  with  blank 
flanges,  or  bled  through  special  openings  beyond  the  valves,  except 
the  particular  pipe  through  which  water  is  to  be  fed  to  the  boiler 
during  the  trial.     During  the  test  the  blow-off  and  feed-pipes  should 
remain  exposed  to  view. 

If  an  injector  is  used,  it  should  receive  steam  directly  through  a 
felted  pipe  from  the  boiler  being  tested.* 

If  the  water  is  metered  after  it  passes  the  injector,  its  temperature 
should  be  taken  at  the  point  where  it  leaves  the  injector.  If  the 
quantity  is  determined  before  it  goes  to  the  injector  the  temperature 
should  be  determined  on  the  suction  side  of  the  injector,  and  if  no 
change  of  temperature  occurs  other  than  that  due  to  the  injector,  the 
temperature  thus  determined  is  properly  that  of  the  feed-water. 
When  the  temperature  changes  between  the  injector  and  the  boiler,  as 
by  the  use  of  a  heater  or  by  radiation,  the  temperature  at  which  the 
water  enters  and  leaves  the  injector  and  that  at  which  it  enters  the 
boiler  should  all  be  taken.  In  that  case  the  weight  to  be  used  is  that 
of  the  water  leaving  the  injector,  computed  from  the  heat-units  if  not 

*  In  feeding  a  boiler  undergoing  test  with  an  injector  taking  steam  from  an- 
other boiler,  or  from  the  main  steam-pipe  from  several  boilers,  the  evaporative  re- 
sults may  be  modified  by  a  difference  in  the  quality  of  the  steam  from  such  source 
compared  with  that  supplied  by  the  boiler  being  tested,  and  in  some  cases  the 
connection  to  the  injector  may  act  as  a  drip  for  the  main  steam-pipe.  If  it  is  known 
that  the  steam  from  the  main  pipe  is  of  the  same  pressure  and  quality  as  that 
furnished  by  the  boiler  undergoing  the  test,  the  steam  may  be  taken  from  such 
main  pipe. 


S36  STEAM-BOILER  ECONOMY. 

directly  measured,  and  the  temperature  that  of  the  water  entering  the- 

boiler. 

Let  w  =  weight  of  water  entering  the  injector. 
x=      "       "  steam       "          "         " 
Aj  =  heat-units  per  pound  of  water  entering  injector. 
h2  =     "       "       "    "    "      "  steam       "  " 

hz  —     "       "       "        "      "  water  leaving        " 

Then,  w  -\-  x  =  weight  of  water  leaving  injector. 

h,  -  h. 

x  =  w  j* p. 

h,  -  hs 

See  that  the  steam -main  is  so  arranged  that  water  of  condensation 
cannot  run  back  into  the  boiler. 

VIII.  Duration  of  Test. — For  tests  made  to  ascertain  either  the 
maximum  economy  or  the  maximum  capacity  of  a  boiler,  irrespective 
of  the  particular  class  of  service  for  which  it  is  regularly  used,  the 
duration  should  be  at  least  10  hours  of  continuous  running.     If  the 
rate  of  combustion  exceeds  25  pounds  of  coal  per  square  foot  of  grate- 
surface  per  hour,  it  may  be  stopped  when  a  total  of  250  pounds  of  coal 
has  been  burned  per  square  foot  of  grate. 

In  cases  where  the  service  requires  continuous  running  for  the 
whole  24  hours  of  the  day,  with  shifts  of  firemen  a  number  of  times 
during  that  period,  it  is  well  to  continue  the  test  for  at  least  24 
hours. 

When  it  is  desired  to  ascertain  the  performance  under  the  working 
conditions  of  practical  running,  whether  the  boiler  be  regularly  in  use 
24  hours  a  day  or  only  a  certain  number  of  hours  out  of  each  24,  the 
fires  being  banked  the  balance  of  the  time,  the  duration  should  not  be 
less  than  24  hours. 

IX.  Starting  and  Stopping  a  Test. — The  conditions  of  the  boiler 
and  furnace  in  all  respects  should  be,  as  nearly  as  possible,  the  same 
at  the  end  as  at  the  beginning  of  a  test.     The  steam-pressure  should 
be  the  same;  the  water-level  the  same;  the  fire  upon  the  grates  should 
be  the  same  in  quantity  and  condition;  and  the  walls,  flues,  etc., 
should  be  of  the  same  temperature.     Two  methods  of  obtaining  the 
desired  equality  of  conditions  of  the  fire  may  be  used,  viz. :  those 
which  were  called  in  the  Code  of  1885  "the  standard  method  "  and 
"  the  alternate  method,"  the  latter  being  employed  where  it  is  incon- 
venient to  make  use  of  the  standard  method.* 

X.  Standard  Method  of  Starting  and  Stopping  a  Test. — Steam 
being  raised  to  the  working  pressure,  remove  rapidly  all  the  fire  from 
the  grate,  close  the  damper,  clean  the  ash-pit,  and  as  quickly  as  pos- 
sible start  a  new  fire  with  weighed  wood  and  coal,  noting  the  time  and 

*Tbe  committee  .concludes  that  it  is  best  to  retain  the  designations  "standard  " 
and  "  alternate,"  since  they  have  become  widely  known  and  established  in  the 
minds  of  engineers  and  in  the  reprints  of  the  Code  of  1885.  Many  engineers  pre- 
fer the  "alternate  "  to  the  "  standard"  method  on  account  of  its  being  less  liable 
to  error  due  to  cooling  of  the  boiler  at  the  beginning  and  end  of  a  test. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  337 

water-level  *  while  the  water  is  in  a  quiescent  state,  just  before 
lighting  the  fire. 

At  the  end  of  the  test  remove  the  whole  fire,  which  has  been  burned 
low,  clean  the  grates  and  ash-pit,  note  the  water-level  when  the 
water  is  in  a  quiescent  state,  and  record  the  time  of  hauling  the  fire. 
The  water-level  should  be  as  nearly  as  possible  the  same  as  at  the  begin- 
ning of  the  test.  If  it  is  not  the  same,  a  correction  should  be  made 
by  computation,  and  not  by  operating  the  pump  after  the  test  is  com- 
pleted. 

XI.  Alternate  Method  of  Starting  and  Stopping  a  Test. — The  boiler 
being   thoroughly  heated  by  a  preliminary  run,  the   fires  are  to  be 
burned  low  and  well  cleaned.     Note  the  amount  of  coal  left  on  the 
grate  as  nearly  as  it  can  be  estimated;  note  the  pressure  of  steam  and 
the  water-level.     Note  the  time,  and  record  it  as  the  starting  time. 
Presh  coal  which  has  been  weighed  should  now  be  fired.     The  ash-pits 
should  be  thoroughly  cleaned  at  once  after  starting.     Before  the  end 
of  the  test  the  fires  should  be  burned  low,  just  as  before  the  start,  and 
the  fires  cleaned  in  such  a  manner  as  to  leave  a  bed  of  coal  on  the 
grates  of  the  same  depth,  and  in  the  same  condition,  as  at  the  start. 
When  this  stage  is  reached,  note  the  time  and  record  it  as  the  stopping 
time.       The   water-level    and   steam- pressures   should   previously   be 
brought  as  nearly  as  possible  to  the  same  point  as  at  the  start.     If  the 
water-level  is  not  the  same  as  at  the  start,  a  correction  should  be  made 
by  computation,  and  not  by  operating  the  pump  after  the  test  is  com- 
pleted. 

XII.  Uniformity  of  Conditions. — In  all  trials  made  to  ascertain 
maximum  economy  or  capacity,  the  conditions  should  be  maintained 
uniformly  constant.     Arrangements  should  be  made  to  dispose  of  the 
steam  so  that  the  rate  of  evaporation  may  be  kept  the  same  from  be- 
ginning to  end.     This  may  be  accomplished  in  a  single  boiler  by  carry- 
ing the  steam  through  a  waste  steam-pipe,  the  discharge  from  which 
can  be  regulated  as  desired.     In  a  battery  of  boilers,  in  which  only 
one  is  tested,  the  draft  may  be  regulated  on  the  remaining  boilers, 
leaving  the  test-boiler  to  work  under  a  constant  rate  of  production. 

Uniformity  of  conditions  should  prevail  as  to  the  pressure  of  steam, 
the  height  of  water,  the  rate  of  evaporation,  the  thickness  of  fire,  the 
times  of  firing,  and  quantity  of  coal  fired  at  one  time,  and  as  to  the 
intervals  between  the  times  of  cleaning  the  fires. 

The  method  of  firing  to  be  carried  on  in  such  tests  should  be  dic- 
tated by  the  expert  or  person  in  responsible  charge  of  the  test,  and 
the  method  adopted  should  be  adhered  to  by  the  fireman  throughout 
the  test. 

XIII.  Keeping  the  Records. — Take  note  of  every  event  connected 
with  the  progress  of  the  trial,  however  unimportant  it  may  appear. 

*  The  gauge-glass  should  not  be  blown  out  within  an  hour  before  the  water- 
level  is  taken  at  the  beginning  and  end  of  a  test,  otherwise  an  error  in  the  reading 
of  the  water-level  may  be  caused  by  a  change  in  the  temperature  and  density  to 
the  water  in  the  pipe  leading  from  the  bottom  of  the  glass  into  the  boiler. 


338  8IEAM-BOILER  ECONOMY. 

Record  the  time  of  every  occurrence  and  the  time  of  taking  every 
weight  and  every  observation. 

The  coal  should  be  weighed  and  delivered  to  the  fireman  in  equal  pro- 
portions, each  sufficient  for  not  more  than  one  hour's  run,  and  a  fresh 
portion  should  not  be  delivered  until  the  previous  one  has  all  been 
fired.  The  time  required  to  consume  each  portion  should  be  noted,  the 
time  being  recorded  at  the  instant  of  firing  the  last  of  each  portion.  It  is 
desirable  that  at  the  same  time  the  amount  of  water  fed  into  the  boiler 
should  be  accurately  noted  and  recorded,  including  the  height  of  .the 
water  in  the  boiler,  and  the  average  pressure  of  steam  and  temperature 
of  feed- water  during  the  time.  By  thus  recording  the  amount  of  water 
evaporated  by  successive  portions  of  coal,  the  test  may  be  divided  into 
several  periods  if  desired,  and  the  degree  of  uniformity  of  combustion, 
evaporation,  and  economy  analyzed  for  each  period.  In  addition  to 
these  records  of  the  coal  and  the  feed-water,  half  hourly  observations 
should  be  made  of  the  temperature  of  the  feed- water,  of  the  flue-gases, 
of  the  external  air  in  the  boiler-room,  of  the  temperature  of  the  fur- 
nace when  a  furnace  pyrometer  is  used,  also  of  the  pressure  of  steam, 
and  of  the  readings  of  the  instruments  for  determining  the  moisture  in 
steam.  A  log  should  be  kept  on  properly  prepared  blanks  containing 
columns  for  record  of  the  various  observations. 

When  the  "standard  method  "  of  starting  and  stopping  the  test 
is  used,  the  hourly  rate  of  combustion  and  of  evaporation  and  the 
horse-power  should  be  computed  from  the  records  taken  during  the 
time  when  the  fires  are  in  active  condition.  This  time  is  somewhat 
less  than  the  actual  time  which  elapses  between  the  beginning  and  end 
of  the  run.  The  loss  of  time  due  to  kindling  the  fire  at  the  beginning 
and  burning  it  out  at  the  end  makes  this  course  necessary. 

XIV.  Quality  of  Steam. — The  percentage  of  moisture  in  the  steam 
should  be  determined  by  the  use  of  either  a  throttling  or  a  separating 
steam  calorimeter.  The  sampling  nozzle  should  be  placed  in  the  ver- 
tical steam-pipe  rising  from  the  boiler.  It  should  be  made  of  ^-inch 
pipe,  and  should  extend  across  the  diameter  of  the  steam-pipe  to  with- 
in half  an  inch  of  the  opposite  side,  being  closed  at  the  end  and  per- 
forated with  not  less  than  twenty  -J-inch  holes  equally  distributed  along 
and  around  its  cylindrical  surface,  but  none  of  these  holes  should  be 
nearer  than  |  inch  to  the  inner  side  of  the  steam-pipe.  The  calorimeter 
and  the  pipe  leading  to  it  should  be  well  covered  with  felting.  When- 
ever the  indications  of  the  throttling  or  separating  calorimeter  show 
that  the  percentage  of  moisture  is  irregular,  or  occasionally  in  excess 
of  3  per  cent,  the  results  should  be  checked  by  a  steam-separator 
placed  in  the  steam-pipe  as  close  to  the  boiler  as  convenient,  with  a 
calorimeter  in  the  steam-pipe  just  beyond  the  outlet  from  the  separ- 
ator. The  drip  from  the  separator  should  be  caught  and  weighed,  and 
the  percentage  of  moisture  computed  therefrom  added  to  that  shown 
by  the  calorimeter. 

Superheating  should  be  determined  by  means  of  a  thermometer 
placed  in  a  mercury-well  inserted  in  the  steam -pipe.  The  degree  of 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  339 

superheating  should  be  taken  as  the  difference  between  the  reading  of 
the  thermometer  for  superheated  steam  and  the  readings  of  the  same 
thermometer  for  saturated  steam  at  the  same  pressure  as  determined 
by  a  special  experiment,  and  not  by  reference  to  steam-tables. 

For  calculations  relating  to  quality  of  steam  and  corrections  for 
quality  of  steam,  see  Appendices  XVIII.  and  XIX. 

XV.  /Sampling  the  Coal  and  Determining  its  Moisture. — As  each 
barrow-load  or  fresh  portion  of  coal  is  taken  from  the  coal-pile,  a  rep- 
resentative shovelful  is  selected  from  it  and  placed  in  a  barrel  or  box 
in  a  cool  place  and  kept  until  the  end  of  the  trial.  The  samples  are 
then  mixed  and  broken  into  pieces  not  exceeding  one  inch  in  diame- 
ter,, and  reduced  by  the  process  of  repeated  quartering  and  crushing 
until  a  final  sample  weighing  about  five  pounds  is  obtained,  and  the 
size  of  the  larger  pieces  are  such  that  they  will  pass  through  a  sieve 
with  £-inch  meshes.  From  this  sample  two  one-quart,  air-tight  glass 
preserving-jars,  or  other  air-tight  vessels  which  will  prevent  the  escape 
of  moisture  from  the  sample,  are  to  be  promptly  filled,  and  these  sam- 
ples are  to  be  kept  for  subsequent  determinations  of  moisture  and  of 
heating  value  and  for  chemical  analyses.  During  the  process  of 
quartering,  when  the  sample  has  been  reduced  to  about  100  pounds,  a 
quarter  to  a  half  of  it  may  be  taken  for  an  approximate  determination 
of  moisture.  This  may  be  made  by  placing  it  in  a  shallow  iron  pan,  not 
over  three  inches  deep,  carefully  weighing  it,  and  setting  the  pan  in 
the  hottest  place  that  can  be  found  on  the  brickwork  of  the  boiler  set- 
ting or  flues,  keeping  it  there  for  at  least  12  hours,  and  then  weighing 
it.  The  determination  of  moisture  thus  made  is  believed  to  be  ap- 
proximately accurate  for  anthracite  and  semi-bituminous  coals,  and 
also  for  Pittsburg  or  Youghiogheny  coal;  but  it  cannot  be  relied 
upon  for  coals  mined  west  of  Pittsburg,  or  for  other  coals  containing 
inherent  moisture.  For  these  latter  coals  it  is  important  that  a  more 
accurate  method  be  adopted.  The  method  recommended  by  the 
committee  for  all  accurate  tests,  whatever  the  character  of  the  coal,  is 
described  as  follows: 

Take  one  of  the  samples  contained  in  the  glass  jars,  and  subject  it 
to  a  thorough  air-drying,  by  spreading  it  in  a  thin  layer  and  exposing 
it  for  several  hours  to  the  atmosphere  of  a  warm  room,  weighing  it 
before  and  after,  thereby  determining  the  quantity  of  surface  moisture 
it  contains.  Then  crush  the  whole  of  it  by  running  it  through  an  or- 
dinary coffee-mill  adjusted  so  as  to  produce  somewhat  coarse  grains 
(less  than  TVmch),  thoroughly  mix  the  crushed  sample,  select  from  it 
a  portion  of  from  10  to  50  grams,  weigh  it  in  a  balance  which  will 
easily  show  a  variation  as  small  as  J  part  in  1000,  and  dry  in  an  air 
or  sand  bath  at  a  temperature  between  240  and  280  degrees  Fahr.  for 
one  hour.  Weigh  it  and  record  the  loss,  then  heat  and  weigh  it 
again  repeatedly,  at  intervals  of  an  hour  or  less,  until  the  minimum 
weight  has  been  reached  and  the  weight  begins  to  increase  by  oxida- 
tion of  a  portion  of  the  coal.  The  difference  between  the  original  and 
the  minimum  weight  is  taken  as  the  moisture  in  the  air-dried  coal. 


340  STEAM-BOILER  ECONOMY. 

This  moisture  test  should  preferably  be  made  on  duplicate  samples, 
•and  the  results  should  agree  within  0.3  to  0.4  of  one  per  cent,  the 
mean  of  the  two  determinations  being  taken  as  the  correct  result. 
The  sum  of  the  percentage  of  moisture  thus  found  and  the  percentage 
of  surface  moisture  previously  determined  is  the  total  moisture.  (Ap- 
pendix XI.) 

XVI.  Treatment  of  Ashes  and  Refuse.  —  The  ashes  and  refuse  are 
to  be  weighed  in  a  dry  state.     If  it  is  found  desirable  to  show  the 
principal  characteristics  of  the  ash,  a  sample  should  be  subjected  to  a 
proximate  analysis  and  the  actual  amount  of  incombustible  material 
determined.     For  elaborate  trials  a  complete  analysis  of  the  ash  and 
refuse  should  be  made. 

XVII.  Calorific  Tests  and  Analysis  of  Coal.  —  The  quality  of  the  fuel 
should  be  determined  either  by  heat-test  or  by  analysis,  or  by  both. 

The  rational  method  of  determining  the  total  heat  of  combustion 
is  to  burn  the  sample  of  coal  in  an  atmosphere  of  oxygen  gas,  the  coal 
to  be  sampled  as  directed  in  Article  XV.  of  this  code. 

The  chemical  analysis  of  the  coal  should  be  made  only  by  an  ex- 
pert chemist.  The  total  heat  of  combustion  computed  from  the  results 
of  the  ultimate  analysis  may  be  obtained  by  the  use  of  Dulong's 
formula  (with  constants  modified  by  recent  determinations),  viz.: 


14,6000  +  62,OOoH  -        +  4000S,  in  which  C,  H,  0,  and  S  refer 

to  the  proportions  of  carbon,  hydrogen,  oxygen,  and  sulphur  respec- 
tively, as  determined  by  the  ultimate  analysis.* 

It  is  desirable  that  a  proximate  analysis  should  be  made,  thereby 
determining  the  relative  proportions  of  volatile  matter  and  fixed  car- 
bon. These  proportions  furnish  an  indication  of  the  leading  charac- 
teristics of  the  fuel,  and  serve  to  fix  the  class  to  which  it  belongs.  As 
an  additional  indication  of  the  characteristics  of  the  fuel,  the  specific 
gravity  should  be  determined. 

XVIII.  Analysis  of  Flue-gases.  —  The  analysis  of  the  flue-gases 
is  an  especially  valuable  method  of  determining  the  relative  value  of 
different  methods  of  firing,  or  of  different  kinds  of  furnaces.  In 
making  these  analyses  great  care  should  be  taken  to  procure  average 
samples  —  since  the  composition  is  apt  to  vary  at  different  points  of  the 
ilue.  The  composition  is  also  apt  to  vary  from  minute  to  minute, 
and  for  this  reason  the  drawings  of  gas  should  last  a  considerable 
period  of  time.  Where  complete  determinations  are  desired,  the 
analyses  should  be  intrusted  to  an  expert  chemist.  For  approximate 
determinations  the  Orsat  f  or  the  Hempel  J  apparatus  may  be  used  by 
the  engineer. 

*Favre  and  Silberman  give  14,544  B.T.U.  per  pound  carbon;  Bertbelot,  14,647 
B.T.U.  Favre  and  Silberman  give  62,032  B.T.U.  per  pound  hydrogen;  Thoinsen, 
61,816  B.T.U. 

f  See  R.  S.  Hale's  paper  on  "Fiue-gas  Analysis,"  Transactions,  vol.  xviii. 
p.  901. 

\  See  Hempel's  "  Methods  of  Gas  Analysis  ''  (Macmillan  &  Co.). 


*  EVAPORATION  TESTS  OF  STFAM-POILEES.  341 

For  the  continuous  indication  of  the  amount  of  carbonic  acid  pres- 
ent in  the  flue-gases,  an  instrument  may  be  employed  which  shows  the 
weight  of  the  sample  of  gas  passing  through  it. 

XIX.  Smoke  Observations. — It  is  desirable  to  have  a  uniform  sys- 
tem of  determining  and  recording  the  quantity  of  smoke  produced 
where  bituminous  coal  is  used.     The  system  commonly  employed  is 
to  express  the  degree  of  smokiness  by  means  of  percentages  dependent 
upon  the  judgment  of  the  observer.     The  committee  does  not  place 
much  value  upon  a  percentage  method,  because  it  depends  so  largely 
upon  the  personal  element,  but  if  this  method  is  used,  it  is  desirable 
that,  so  far  as  possible,  a  definition  be  given  in  explicit  terms  as  to  the 
basis  and  method  employed  in  arriving  at  the  percentage.     The  actual 
measurement  of  a  sample  of  soot  and  smoke  by  some  form  of  meter  is 
to  be  preferred. 

XX.  Miscellaneous. — In  tests  for  purposes  of  scientific  research,  in 
which  the  determination  of  all  the  variables  entering  into  the  test  is 
desired,  certain  observations  should  be  made  which  are  in  general  un- 
necessary for  ordinary  tests.     These  are  the  measurement  of  the  air- 
supply,  the  determination  of  its  contained  moisture,  the  determination 
of  the  amount  of  heat  lost  by  radiation,  of  the  amount  of  infiltration  of 
air  through  the  setting,  and   (by  condensation  of  all  the  steam  made 
by  the  boiler)  of  the  total  heat  imparted  to  the  water. 

As  these  determinations  are  rarely  undertaken,  it  is  not  deemed 
advisable  to  give  directions  for  making  them. 

XXI.  Calculations  of  Efficiency. — Two  methods  of  defining  and 
calculating  the  efficiency  of  a  boiler  are  recommended.     They  are: 

Heat  absorbed  per  Ib.  combustible 

1.  Efficiency  of  the  boiler  =  7T1 — r^—  — ^ 

Calonfic  value  ot  1  Ib.  combustible. 

.  ,,     ,.,  Heat  absorbed  per  Ib.  coal 

2.  Efficiency  of  the  boiler  and  grate  =  ^  -. — ^ — 

Calorific  value  ot  1  Ib.  coal. 

The  first  of  these  is  sometimes  called  the  efficiency  based  on  com- 
bustible, and  the  second  the  efficiency  based  on  coal.  The  first  is 
recommended  as  a  standard  of  comparison  for  all  tests,  and  this  is  the 
one  which  is  understood  to  be  referred  to  when  the  word  "  efficiency  " 
alone  is  used  without  qualification.  The  second,  however,  should  be 
included  in  a  report  of  a  test,  together  with  the  first,  whenever  the 
object  of  the  test  is  to  determine  the  efficiency  of  the  boiler  and  fur- 
nace together  with  the  grate  (or  mechanical  stoker),  or  to  compare 
different  furnaces,  grates,  fuels,  or  methods  of  firing. 

The  heat  absorbed  per  pound  of  combustible  (or  per  pound  coal)  is 
to  be  calculated  by  multiplying  the  equivalent  evaporation  from  and 
at  212  degrees  per  pound  combustible  (or  coal)  by  965.7. 

XXII.  The  Heat  Balance. — An  approximate  "heat  balance,"  or 
statement  of  the  distribution  of  the  heating  value  of  the  coal  among 


342 


STEAM-BOILER  ECONOMY. 


the  several  items  of  heat  utilized  and  heat  lost  may  be  included  in  the 
report  of  a  test  when  analyses  of  the  fuel  and  of  the  chimney-gases 
have  been  made.  It  should  be  reported  in  the  following  form : 

HEAT  BALANCE,  OR  DISTRIBUTION  OF  THE  HEATING  VALUE  OF  THE  COMBUSTIBLE. 
Total  Heat  Value  of  1  Ib.  of  Combustible B.T.U. 


B.T.U. 

Per  Cent. 

1. 

2. 

3. 

4. 
5. 

6. 

Heat  absorbed  by  the  boiler  =  svaporation  from  and  at  212 
degrees  per  pound  of  combustible  X  965.7. 
Loss  due  to  moisture  in  coal  =  per  cent  of  moisture  referred 
to  combustible  -5-  100  X  [(212—  t)  +  966  +  0.48  (T  - 
212)]  (t  =  temperature  of  air  in  the  boiler-room,  T  = 
that  of  the  flue-gases). 
Loss  due  to  moisture  formed  by  the  burning  of  hydrogen 
—  per  cent  of  hydrogen  to  combustible  -5-  100  X  9  X 
[(212  -  0+  966  +  0.48  (T  -  212)]. 
*  Loss  due  to  heat  carried  away  in  the  dry  chimney-gases  = 
weight  of  gas  per  pound  of  combustible  X  Q.24x(T—t). 
CO 

100.00 

COj  -}-  CO 
per  cent  C  in  combustible  vx  1A  1RA 

100 
Loss  due  to  unconsuined    hydrogen   and  hydrocarbons,   to 
heating  the  moisture  in  the  air,  to  radiation,  and  unac- 
counted for.     (Some  of  these  losses  may  be  separately 
itemized  if  data  are  obtained  from  which  they  may  be 
calculated.) 

XXIII.  Report  of  the  Trial — The  data  and  results  should  be  re- 
ported in  the  manner  given  in  either  one  of  the  two  following  tables, 
omitting  lines  where  the  tests  have  not  been  made  as  elaborately  as  pro- 
vided for  in  such  tables.  Additional  lines  may  be  added  for  data  re- 
lating to  the  specific  object  of  the  test.  The  extra  lines  should  be 
classified  under  the  headings  provided  in  the  tables,  and  numbered  as 
per  preceding  line,  with  subletters  a,  b,  etc.  The  Short  Form  of 
Report,  Table  No.  2,  is  recommended  for  commercial  tests  and  as  a 
convenient  form  of  abridging  the  longer  form  for  publication  when 
saving  of  space  is  desirable.  For  elaborate  trials,  it  is  recommended 
that  the  full  log  of  the  trial  be  shown  graphically,  by  means  of  a  chart. 

*  The  weight  of  gas  per  pound  of  carbon  burned  may  be  calculated  from  the  gas  analyses  a8 
follows: 

Dry  gas  per  pound  carbon  =   lic°a  +  8O  +  7(CO  +  N)  >  .Q  wWch  co     CQ  Q  ftnd  N  ape  tfae 

O  Vi^vJfl  ~T~  vyV-JJ 

percentages  by  volume  of  the  several  gases.  As  the  sampling  and  analyses  of  the  gases  in  the 
present  state  of  the  art  are  liable  to  considerable  errors,  the  result  of  this  calculation  is  usually 
only  an  approximate  one.  The  heat  balance  itself  is  also  only  approximate  for  this  reason,  as 
well  as  for  the  fact  that  it  is  not  possible  to  determine  accurately  the  percentage  of  unburned 
hydrogen  or  hydrocarbons  in  the  flue-gases. 

The  weight  of  dry  gas  per  pound  of  combustible  is  found  by  multiplying  the  dry  gas  per 
pound  of  cai-bon  by  the  percentage  of  carbon  in  the  combustible,  and  dividing  by  100. 

t  COa  and  CO  are  respectively  the  percentage  by  volume  of  carbonicacid  and  carbonic  oxide 
in  the  flue-gases.  The  quantity  10.150  =  No.  heat-units  generated  by  burning  to  carbonic  acid 
one  pound  of  carbon  contained  in  carbonic  oxide. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  343 

TABLE   NO.    1. 
DATA  AND  RESULTS  OF  EVAPORATIVE  TEST. 

Arranged  in  accordance  with  the  Complete  Form  advised  by  the  Boiler  Test  Com- 
mittee of  the  American  Society  of  Mechanical  Engineers.     Code  of  1899. 

Made  by of boiler  at to 

determine. 

Principal  conditions  governing  the  trial 


Kind  of  fuel* 

Kind  of  furnace 

State  of  the  weather 

Method  of  starting  and  stopping  the  test  ("  standard  "  or  "alternate,"  Art.  X. 
and  XI.,  Code) 

1.  Date  of  trial. . 

2.  Duration  of  trial hours. 

Dimensions  and  Proportions. 

(A  complete  description  of  the  boiler,  and  drawings  of  the  same  if  of  unusual 
type,  should  be  given  on  an  annexed  sheet.     (See  Appendix  X.) 

3.  Grate-surface width length area sq.  ft. 

4.  Height  of  furnace ins. 

5.  Approximate  width  of  air-spaces  in  grate in. 

6.  Proportion  of  air  space  to  whole  grate-surface per  cent. 

7.  Water-heating  surface sq.  ft. 

8.  Superheating  surface " 

9.  Ratio  of  water-heating  surface  to  grate-surface —  to  1. 

10.  Ratio  of  minimum  draft  area  to  grate-surface 1  to  — 

Average  Pressures. 

11 .  Steam-pressure  by  gauge .Ibs.  persq.  in. 

12.  Force  of  draft  between  damper  and  boiler ins.  of  water. 

13.  Force  of  draft  in  furnace. "  " 

14.  Force  of  draft  or  blast  in  ash-pit "  " 

Average  Temperatures. 

15.  Of  external  air deg. 

16.  Of  fire-room 

1 7.  Of  steam 

18-  Of  feed- water  entering  heater 

19.  Of  feed-water  entering  economizer 

20.  Of  feed-water  entering  boiler 

21 .  Of  escaping  gases  from  boiler 

22.  Of  escaping  gases  from  economizer 

Fuel. 

23.  Size  and  condition 

24.  Weight  of  wood  used  in  lighting  fire Ibs. 

25.  Weight  of  coal  as  fired  \ 

"26.  Percentage  of  moisture  in  coal\ per  cent. 

*  The  items  printed  in  italics  correspond  to  the  items  in  the  "  Short  Form  of  Code." 
t  Including  equivalent  of  wood  used  in  lighting  the  fire,  not  including  unburnt  coal  withdrawn 
from  furnace  at  times  of  cleaning  and  at  end  of  test.  One  pound  of  wood  is  taken  to  be  equal 
to  0.4  pound  of  coal,  or,  in  case  greater  accuracy  is  desired,  as  having  a  heat  value  equivalent 
to  the  evaporation  of  6  pounds  of  water  from  and  at  212  degrees  per  pound.  (6  X  965.7  =  5794 
B.T.U.)  The  term  "  as  fired  "  means  in  its  actual  condition,  including:  moisture. 

tThis  is  the  total  moisture  in  the  coal  as  found  by  drying  it  artiflcally,  as  described  in 
.Art.  XV.  of  Code. 


344  STEAM-BOILER  ECONOMY. 

27.  Total  weight  of  dry  coal  consumed Ibs. 

28.  Total  ash  and  refuse " 

29.  Quality  of  ash  and  refuse 

30.  Total  combustible  consumed Ibs. 

31.  Percentage  of  ash  and  refuse  in  dry  coal per  cent., 

Proximate  Analysis  of  Coal. 

Of  Coal.     Of  Combustible. 

32.  Fixed  carbon per  cent.  per  cent. 

33.  Volatile  matter 

34.  Moisture "  

35.  Ash.. , "  


100  per  cent.      100  per  cent* 

36.  Sulphur,  separately  determined "  " 

Ultimate  Analysis  of  Dry  Coal. 

Of  Coal.     Of  Combustible. 

37.  Carbon per  cent.        per  cent. 

38.  Hydrogen. 

39.  Oxygen 

40.  Nitrogen 

41.  Sulphur 

42.  Ash 


100  per  cent.     100  per  cent. 

43.  Moisture  in  sample  of  coal  as  received "  " 

Analysis  of  Ash  and  Refuse. 

44.  Carbon per  cent. 

45.  Earthy  matter " 

Fuel  per  Hour. 

46.  Dry  coal  consumed  per  hour Ibs. 

47.  Combustible  consumed  per  hour " 

48.  Dry  coal  per  square  foot  of  grate- surf  ace  per  hour " 

49.  Combustible  per  square  foot  of  water-heatipg  surface  per  hour. .  " 

Calorific  Value  of  Fuel. 

50.  Calorific  value  by  oxygen  calorimeter,  per  Ib.  of  dry  coal B.T.F.. 

51.  Calorific  value  by  oxygen  calorimeter,  per  Ib.  of  combustible '  *  ' '  " 

52.  Calorific  value  by  analysis,  per  Ib.  of  dry  coal  * "  "  '* 

53.  Calorific  value  by  analysis,  per  Ib.  of  combustible "  "  " 

Quality  of  Steam. 

54.  Percentage  of  moisture  in  steam per  cent.. 

55.  Number  of  degrees  of  superheating deg. 

66.  Quality  of  steam  (dry  steam  =  unity).     (For  exact  determination 

of  the  factor  of  correction  for  quality  of  steam  see  Appendix 
XVIII.) 

Water. 

57.  Total  weight  of  water  fed  to  boiler  \ v  . . .  Ibs. 

58.  Equivalent  water  fed  to  boiler  from  and  at  212  degrees *. . . .  " 

69.   Water  actually  evaporated,  corrected  for  quality  of  steam ,. .  " 

*  S*»e  formula  for  calorific  value  under  Article  XVII.  of  fi-de. 

t  Corrected  fur  inequality  of  water-level  and  of  steain-presBtir*»  at  beginning  and  end  of  test. 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


345 


60.  Factor  of  evaporation  * Ibs. 

61.  Equivalent  water  evaporated  into   dry  steain   from  and   at   212 

degrees.f     (Item  59  x  Item  60.) 

Water  per  Hour. 

62.  Water  evaporated  per  hour,  corrected  for  quality  of  steam " 

63.  Eqivalent  evaporation  per  hour  from  and  at  212  degrees^ " 

64.  Equivalent  evaporation  per  hour  from  and  at  212  degrees  per 

square  foot  of  water-heating  surface  \ " 

Horse- power. 

65.  Horse-power  developed.     (34£  Ibs.  of  water  evaporated  per  hour 

into  dry  steam  from  and  at  212   degrees,   equals  one  horse- 
power} \ H.P. 

66.  Builders'  rated  horse-power " 

67.  Percentage  of  builders'  rated  horse-power  developed per  cent.. 

Economic  Results. 

68.  Water  apparently  evaporated  under  actual  conditions  per  pound 

of  coal  as  fired.     (Item  58-Wfera  25.) Ibs. 

69.  Equivalent  evaporation  from   and  at  212  degrees  per  pound  of 

coal  as  fired.\    (Item  61  -5-  Item  25  ) .  .  " 

70.  Equivalent  evaporation  from  and  at  212  degrees  per  pound  of  dry 

coal.\     (Item  61  -f-  Item  27.) " 

71.  Equivalent  evaporation  from  and  at  212  degrees  per  pound  of 

combustible.]     (Item  61  ^  Item  30.) " 

(If  the  equivalent  evaporation,  Items  69,  70,  and  71,  is  not  cor- 
rected for  the  quality  of  steam,  the  fact  should  be  stated.) 

Efficiency. 

72.  Efficiency  of  the  boiler  ;  heat  absorbed  by  the  boiler  per  Ib.  of  com- 

bustible di>  ided  by  the  heat-value  of  one  Ib.  of  combustible  § per  cent.. 

73.  Efficiency  of  boiler,  including   the   grate ;   heat  absorbed  by  the 

boiler,  per  Ib.  of  dry  coal,  divided  by  the  heat-value  of  one  Ib.  of 
dry  coal " 

Cost  of  Evaporation. 

74.  Cost  of  coal  per  ton  of Ibs.  delivered  in  boiler-room $ 

75.  Cost  of  fuel  for  evaporating  1000  Ibs.  of  water  under  observed 

conditions $ 

76.  Cost  of  fuel  used  for  evaporating  1000  Ibs.  of  water  from  and  at 

212  degrees $ 

Smoke  Observations. 

77.  Percentage  of  smoke  as  observed per  cent. 

78.  Weight  of  soot  per  hour  obtained  from  smoke-meter ounces. 

79.  Volume  of  soot  per  hour  obtained  from  smoke-meter cub.  in. 


TJ      T. 

*  Factor  of  evaporation  =          „    ,  in  which  H  and  h  are  respectively  the  total  heat  in  steam 

of  the  average  observed  pressure,  and  in  water  of  the  average  observed  temperature  of  the 
feed. 

t  The  symbol  "  U.  E.,"  meaning  "  Units  of  Evaporation."  may  be  conveniently  substituted 
for  the  expression  "  Equivalent  water  evaporated  into  dry  steam  from  and  at  212  degrees,"  its 
definition  being  given  in  a  foot-note. 

\  Held  to  be  the  equivalent  of  30  Ibs.  of  water  per  hour  evaporated  from  100  degrees  Fiihr. 
into  dry  steam  at  70  Ibs.  gauge-pressiire.  (See  Introduction  to  Code.) 

§  In  all  cases  where  the  word  "combustible"  is  used,  it,  means  the  coal  without  moisture 
snd  nsli.  but  inclii'lii'g  all  other  constituents.  It  is  the  same  as  what  is  called  in  Europe  "  coal 
dry  and  free  from  ash.1' 


346  STEAM-BOILEll  ECONOMY. 

Methods  of  Firing. 

80.  Kind  of  firing  (spreading,  alternate,  or  coking) 

81.  Average  thickness  of  fire 

82.  Average  intervals  between  firings  for  each  furnace  during  time 

when  fires  are  in  normal  condition 

83.  Average  interval  between  times  of  levelling  or  breaking  up 

Analyses  of  tJie  Dry  Gases. 

84.  Carbon  dioxide  (CO2) per  cent. 

85.  Oxygen  (O) 

86.  Carbon  monoxide  (CO) 

87.  Hydrogen  and  hydrocarbons 

88.  Nitrogen  (by  difference)  (N) 

100  per  cent. 

TABLE  NO.   2. 
DATA  AND  BESULTS  OF  EVAPORATIVE  TEST, 

Arranged  in  accordance  with  the  Short  Form  advised  by  the  Boiler-test  Commit- 
tee of  the  American  Society  of  Mechanical  Engineers.     Code  of  1899. 

Made  by on boiler,  at to 

determine 

Kind  of  fuel 

Kind  of  furnace , 

Method  of  starting  and  stopping  the  test  ("standard  "  or  "alternate,"  Art.  X. 

and  XI.,  Code) 

Grate-surface sq.  ft. 

Water-heating  surface 

Superheating  surface 

Total  Quantities. 

1.  Date  of  trial 

2.  Duration  of  trial hours. 

3.  Weight  of  coal  as  fired* Ibs. 

4.  Percentage  of  moisture  in  coal  * per  cent. 

5.  Total  weight  of  dry  coal  consumed Ibs. 

6.  Total  ash  and  refuse " 

7.  Percentage  of  ash  and  refuse  in  dry  coal per  centr 

8.  Total  weight  of  water  fed  to  the  boiler  * Ibs. 

9.  Water  actually  evaporated,  corrected  for  moisture  or  super- 

heat in  steam ,. " 

10.  Equivalent  water  evaporated  into  dry  steam  from  and  at  212 

degrees* " 

Hourly  Quantities. 

11.  Dry  coal  consumed  per  hour Ibs. 

12.  Dry  coal  per  square  foot  of  grate-surface  per  hour " 

13.  Water  evaporated  per  hour  corrected  for  quality  of  steam. ...  " 

14.  Equivalent  evaporation  per  hour  from  and  at  212  degrees  *...  " 

15.  Equivalent  evaporation  per  hour  from  and  at  212  degrees  per 

square  foot  of  water-heating  surface  * " 

*  See  foot-notes  of  Complete  Form. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  347 

Average  Pressures,  Temperatures,  etc. 

1 6.  Steam-pressure  by  gauge Ibs.  per  sq.  in. 

17.  Temperature  of  feed-water  entering  boiler deg. 

1  8.   Temperature  of  escaping  gases  from  boiler 

19.  Force  of  draft  between  damper  and  boiler ins.  of  water. 

20.  Percentage  of   moisture  in  steam,  or  number  of  degrees   of 

superheating per  cent,  or  deg. 

Horse-power. 

21.  Horse-power  developed.     (Item  14 -5- 34^)* H.P. 

22.  Builders'  rated  horse-power  

23.  Percentage  of  builders'  rated  horse-power  developed per  cent. 

Economic  Results. 

24.  Water  apparently  evaporated    under   actual    conditions   per 

pound  of  coal  as  fired.     (Item  8  -j-  Item  3) Ibs. 

25.  Equivalent  evaporation  from  and  at  212  degrees  per  pound  of 

coal  as  fired.*    (Item  9  -=-  Item  3) " 

26.  Equivalent  evaporation  from  and  at  212  degrees  per  pound  of 

dry  coal.*     (Item  9  H- Item  5) " 

27.  Equivalent  evaporation  from  and  at  212  degrees  per  pound  of 

combustible.*    [Item  9  -f-  (Item  5  —  Item  6)  ] " 

(If  Items  25,  26,  and  27  are  not  corrected  for  quality  of  steam, 
the  fact  should  be  stated.) 

Efficiency. 

28.  Colorific  value  of  the  dry  coal  per  pound B.T.U. 

29.  Calorific  value  of  the  combustible  per  pound "    "    " 

30.  Efficiency  of  boiler  (based  on  combustible)  * per  cent. 

31.  Efficiency  of  boiler,  including  grate  (based  on  dry  coal) " 

Cost  of  Evaporation. 

32.  Cost  of  coal  per  ton  of Ibs.  delivered  in  boiler-room $ 

33.  Cost  of  coal  required  for  evaporating  1000  pounds  of  water 

from  and  at  212  degrees $ 

*  See  foot-notes  of  Complete  Form. 


34:8  STEAM-BOILER  ECONOMY. 


APPENDICES  TO  CODE  OF  1899.* 

*  Greatly  condensed  from  the  original  report.  Many  of  the  appendices  in  the 
report  are  omitted,  and  others  are  abridged.  The  initials  signed  to  the  appendices 
are  those  of  the  members  of  the  committee  by  whom  they  were  written,  viz.: 
Charles  E.  Emery,  Chas.  T.  Porter,  Geo.  H.  Barrus,  and  William  Kent;  or  of  J.  C. 
Hoadley,  deceased,  member  of  the  committee  of  1885. 

APPENDIX  I. 

RELATIVE   WEIGHTS   OF   WATER  AND   FUEL.      • 

The  elaborate  directions  and  multiplicity  of  details  provided  for  in 
the  foregoing  Code  should  not  divert  the  minds  of  amateurs  from  the 
fact  that  the  principal  elements  to  be  ascertained  in  a  boiler  test  are- 
the  weight  of  water  evaporated  and  the  weight  of  the  fuel  required  to 
produce  such  evaporation.  If  the  Code  be  scanned  closely  with  this 
thought  in  mind,  it  will  be  found  that  many  of  the  elaborate  provis- 
ions are  intended  to  secure  accuracy  in  determining  these  important 
elements.  It  is  true  that  there  are  provisions  embodied  which  do  not 
refer  directly  thereto,  but  it  is  necessary  that  all  available  data  be  ob- 
tained so  that  comparisons  can  be  made  with  the  performances  of 
other  boilers,  for  the  purpose  of  adjusting  contracts,  for  general 
information,  as  a  guide  in  the  selection  of  fuel,  or  for  improvements 
in  the  future.  c.  E.  E. 

APPENDIX  II. 

OBJECT   OF   THE   TEST. 

In  preparing  for  and  conducting  trials  of  steam-boilers,  the  speci- 
fic object  of  the  proposed  trial  should  be  clearly  defined  and  steadily 
kept  in  view. 

1.  If  it  be  to  determine  the  efficiency  of  a  given  style  of  boiler  or 
of   boiler-setting   under   normal   conditions,    the   boiler,  brickwork, 
grates,  dampers,  flues,  pipes,  in  short  the  whole  apparatus  should  be- 
carefully  examined  and  accurately  described,  and  any  variation  from 
a  normal  condition  should  be  remedied  if  possible,  and,  if  irremediable, 
clearly  described  and  pointed  out. 

2.  If  it  be  to  ascertain  the  condition  of  a  given  boiler  or  set  of 
boilers  with  a  view  to  the  improvement  of  whatever  may  be  faulty, 
the   conditions  actually   existing  should  be  accurately  observed  and 
clearly  described. 

3.  If  the  object  be  to  determine  the  relative  value  of  two  or  more 
kinds  of  coal,  or  the  actual  value  of  any  kind,  exact  equality  of  con- 


EVAPOHATION  TESTS  OF  STEAM-BOILERS.  349 

ditious  should  be  maintained  if  possible,  or,  where  that  is  not  prac- 
ticable, all  variations  should  be  duly  allowed  for. 

4.  Only  one  variable  should  be  allowed  to  enter  into  the  problem; 
or,  since  the  entire  exclusion  of  disturbing  variations  cannot  usually 
be  effected,  they  should  be  kept  as  closely  as  possible  within  narrow 
limits,  and  allowed  for  with  all  possible  accuracy. 

j.  c.  H. 

APPENDIX  III. 

GENERAL   OBSERVATIONS. 

All  observations  are  to  be  made  by  the  expert,  either  personally  or 
by  his  assistants.  No  statement  of  any  kind  is  to  be  received  from 
the  owner  or  persons  in  charge  of  the  boiler.  All  possibility  of  any- 
thing that  would  falsify  the  results  must  be  closely  guarded  against; 
all  pipes  not  used  must  be  taken  away  or  blank  flanges  inserted. 

A  system  of  firing  and  a  system  of  measuring  the  feed-water  should 
be  employed  that  will  prove  the  correctness  of  the  record,  and,  if 
errors  are  made,  will  clearly  expose  them. 

If  possible  the  steam  generated  should  be  condensed  by  passing  it 
through  a  surface-condenser,  where  it  is  cooled  by  a  strong  current  of 
water  in  a  closed  chamber.  By  this  means  the  number  of  thermal 
units  added  may  be  ascertained  with  precision. 

A  boiler-test  cannot  be  conducted  properly  when  it  is  complicated 
by  being  combined  with  an  engine-test. 

c.  T.  p. 

APPENDIX  IV. 

PRECAUTIONS   TO    BE    OBSERVED    IN    MAKING    A    BOILER-TEST. 

Boiler- tests  are  often  undertaken  witli  insufficient  apparatus  and 
assistance.  It  is  possible  for  a  single  person  to  test  one  boiler,  or  even 
several  in  a  battery,  but  it  requires  a  great  deal  of  labor  to  do  so,  and  in 
many  cases  such  person  would  be  so  fatigued  as  to  be  liable  to  make  a 
simple  error  vitiating  the  results.  He  would,  moreover,  at  no  time  be 
able  to  give  proper  oversight  to  the  test,  so  as  to  prevent  accidental  or 
unauthorized  interferences.  It  is  very  desirable,  in  fact  almost  indis- 
pensable, that  an  assistant  be  detailed  to  weigh  the  coal,  and  another 
to  weigh  or  measure  the  water;  if  calorimeter  tests  are  to  be  under- 
taken, still  another  assistant  should  be  provided.  The  engineer  in 
charge  is  then  left  free  to  oversee  the  work  of  all,  and  relieve  either 
temporarily  when  necessary.  Engineers  are  frequently  called  upon  to 
make  boiler-trials  in  connection  with  parties  whose  interests  are  an- 
tagonistic to  a  fair  test,  and  frequently  the  voluntary  assistance  of 
busybodies  is  likely  to  produce  errors  in  the  results.  It  is  therefore 
essential  to  have  trustworthy  assistants,  and  those  of  sufficient  calibre 
not  to  be  confused  by  interested  parties,  who  will  frequently  en- 


350  S1EAU-BOILER  ECONOMY. 

deavor,  in  the  most  plausible  manner,  to  make  out  that  a  certain 
measure  of  coal  has  been  already  tallied,  or  that  a  certain  tank  of 
water  has  not  been  tallied. 

In  the  first  engine-trials  at  the  American  Institute  Exhibition 
(1869),  in  the  Centennial  boiler-trials  (1876),  and  since  in  private 
trials  respecting  performances  of  boilers  as  between  the  contractor  and 
purchaser,  the  writer  has  arranged  for  both  interests  to  take  the  data 
at  the  same  moment,  with  instructions,  if  agreement  could  not  be  had, 
that  the  difference  be  at  once  referred  to  him. 

In  weighing  the  coal,  the  barrow  or  vessel  used  should  be  balanced 
on  a  scale  and  then  filled  to  a  certain  definite  weight.  The  laborer 
will  soon  learn  to  fill  a  vessel  to  the  same  weight  within  a  few  pounds 
by  counting  the  number  of  shovels  thrown  in,  when  the  change  of  a 
lump  or  two  to  or  from  a  small  box  alongside  the  scale  will  balance  it. 

The  water  may  be  measured  in  one  tank  by  filling  it  to  one  mark 
and  pumping  down  to  another,  but  this  involves  stopping  the  pump 
when  filling  the  tank,  thereby  failing  to  maintain  uniformity  of  con- 
ditions. Two  tanks  arranged  so  that  each  can  be  filled  and  emptied 
alternately  are  much  better.  A  still  better  plan  is  to  have  a  settling- 
tank  to  pump  from  and  a  measuring- tank  which  is  emptied  into  it, 
and  this  plan  is  improved  by  setting  the  measuring-tank  on  a  scale, 
and  actually  weighing  the  water.  For  large  operations  three  tanks 
are  necessary:  a  lower  tank  to  pump  from  and  two  measuring- tanks, 
one  of  which  is  filling  while  the  other  is  being  emptied. 

A  simple  tally  should  never  be  trusted.  Nothing  seems  more  re- 
liable to  an  inexperienced  observer  than  to  mark  1,  2,  3,  4,  with  a  di- 
agonal cross  mark  for  5 ;  but  when  there  are  waits  of  several  minutes 
between  the  marks,  and  several  operations  performed  after  a  tally  is 
made,  there  will  be  confusion  in  the  mind  whether  or  not  the  tally  has 
been  actually  made.  The  tallies  both  of  weights  of  coal  and  of  tanks 
of  water  should  be  written  on  separate  lines,  the  time  noted  opposite 
each,  and  the  records  always  made  at  the  beginning  or  termination  of 
some  particular  operation;  for  instance,  in  weighing  coal  at  the  time 
only  when  the  barrel  or  bucket  is  dumped  on  the  fire-room  floor.  It 
is  desirable  to  have  a  number  of  coincident  records  of  coal  and  water 
throughout  the  trial,  so  that  in  case  of  accident  it  may  be  held  to  have 
ended  at  one  of  such  times.  The  uniformity  of  the  operations  may 
also  be  tested  in  this  way  from  time  to  time.  For  this  reason  it  will 
be  found  convenient  to  fire  from  a  wheel-barrow  set  on  a  scale  and  to 
have  a  float  or  water-gauge  connected  with  the  tank  from  which  the 
water  is  pumped ;  by  which  means  the  coal  and  water  used  may,  in  an 
evident  way,  be  ascertained  for  any  desired  interval. 

c.  E.  E. 

APPENDIX  X. 

DESCRIPTION    OF    BOILER. 

The  report  should  include  a  complete  description  of  the  boiler, 
Which,  for  special  boilers,  should  be  written  out  at  length,  but  gener- 


EVAPORATION  TESTS   OF  STEAM-BOILERS.  351 

ally  can    conveniently  be  presented  in  tabular  form  substantially  aa 
follows : 

Type  of  boiler;  diameter  of  shell;  length  of  shell;  number  of 
tubes;  diameter  of  tubes;  length  of  tubes;  diameter  of  steam-drum; 
width  of  furnace;  length  of  furnace;  kind  of  grate-bars;  width  of  air- 
spaces; ratio  of  area  of  grate  to  area  of  air-spaces;  area  of  chimney; 
height  of  chimney;  length  of  flues  connecting  to  chimney;  area  of 
flues  connecting  to  chimney. 

Governing  proportions:  Grate-surface;  heating  surface  (water, 
steam,  total);  area  of  draft  through  or  between  tubes;  ratio  grate  to 
heating  surface;  ratio  draft-area  to  grate;  ratio  draft-area  to  total 
heating  surface;  water-space;  steam-space;  ratio  grate  to  water-space \ 
ratio  grate  to  steam-space. 

c.  E.  E. 

APPENDIX  XL 

DETEEMIKIKG    THE    MOISTUKE    IX    COAL. 

Until  recently  two  methods  of  determining  moisture  in  coal  have 
been  in  common  use:  first,  the  one  usually  adopted  in  boiler-testing, 
which  consists  in  drying  a  large  sample,  fifty  pounds  or  more,  in  a 
shallow  pan  placed  over  the  boiler  or  flue;  second,  the  method  usually 
followed  by  chemists,  of  drying  a  one-gram  sample  of  pulverized  coal 
at  212°  F.,  or  a  little  above,  for  an  hour,  or  until  constant  weight  is 
obtained.  Both  methods  are  liable  to  large  errors.  In  the  first 
method,  the  temperature  at  which  the  drying  takes  place  is  uncertain, 
and  there  is  no  means  of  knowing  whether  the  temperature  obtained 
is  sufficient  to  drive  off  the  moisture  that  is  held  by  capillary  force 
or  other  attraction  within  the  lumps  of  coal,  which,  at  least  in  case  of 
bituminous  coals,  seem  to  be  as  porous  as  wood,  and  as  capable  of  ab- 
sorbing moisture  from  the  atmosphere.  The  second  method  is  liable 
to  greater  errors  in  sampling  than  the  first,  and  during  the  process  of 
fine  crushing  and  passing  through  sieves,  a  considerable  portion  of  the 
moisture  is  apt  to  be  removed  by  air-drying.  In  an  extensive  series  of 
boiler-tests  made  by  the  writer  in  the  summer  of  1896,  it  became 
necessary  to  find  more  accurate  means  of  determining  moisture  than 
either  of  those  above  described.  It  was  found  by  repeated  heat- 
ing at  gradually  increasing  temperatures  from  212°  up  to  300°  or 
over,  and  weighing  at  intervals  of  an  hour  or  more,  that  the  weight  of 
coal  continually  decreased  until  it  became  nearly  constant,  and  then  a 
very  slight  increase  took  place,  which  increase  became  greater  on  further 
repeated  heatings  to  temperatures  above  250°.  It  has  often  been  stated 
that  if  coal  is  heated  above  212°  F.,  volatile  matter  will  be  driven  off; 
but  repeated  tests  on  seventeen  different  varieties  of  coal  mined  in 
western  Pennsylvania,  Ohio,  Indiana,  Illinois,  and  Kentucky  invariably 
showed  a  gradual  decrease  of  weight  to  a  minimum,  followed  by  the 
increase,  as  stated  above,  and  in  no  single  case  was  there  any  percept- 
ible odor  or  other  indication  of  volatile  matter  passing  off  below  a  tern- 


352  STEAM-BOILER  ECONOMY. 

perature  of  350°.  The  fact  that  no  volatile  matter  was  given  off  was 
further  proved  by  heating  the  coal  in  a  glass  retort  and  catching  the 
vapor  driven  off  in  a  bottle  filled  with  water  and  inverted  in  a  basin ; 
the  air  displaced  from  the  retort  by  expansion  due  to  the  heating  dis- 
placing the  water  in  the  bottle.  When  the  retort  was  cooled,  after 
being  heated  to  350°  in  an  oil  bath,  the  air  thus  expanded  contracted, 
#nd  returned  from  the  bottle  to  the  retort,  leaving  the  bottle  full  of 
water,  as  at  the  beginning  of  the  heating,  showing  that  no  gas  had 
l>een  given  off,  except  possibly  such  exceedingly  small  amount  as 
might  be  absorbed  by  the  water.  The  method  described  in  Section 
XV.  of  the  report  was  then  adopted  as  the  best  available  method  of 
determining  the  moisture  in  these  coals.  Its  accuracy  was  further 
checked  by  other  methods.* 

The  new  method  of  drying  and  its  results  were  communicated  by 
the  writer  to  Prof.  R.  0.  Carpenter  of  Cornell  University,  shortly 
after  they  were  made,  and  he  thereupon  began  experimenting  with 
the  method,  and  fully  confirmed  the  writer's  conclusions.  In  a  letter 
dated  May  18,  1897,  he  says:  "We  have  investigated  the  moisture 
question,  and  find  that  in  all  the  samples  tested,  some  four  or  five  in 
number,  there  is  no  appreciable  loss  between  temperatures  250  and  350 
degrees;  at  least  the  loss  is  less  then  our  means  of  weighing."  In  his 
paper  on  ' '  Hygrometric  Properties  of  Coals,"  presented  at  the  Hart- 
ford meeting  (Transactions,  vol.  xviii.  p.  948),  he  says: 

"  With  the  most  volatile  coals,  there  is  no  sensible  loss  of  weight 
due  to  driving  off  the  volatile  matter  under  a  temperature  of  380° 
Fahr.,  and  with  anthracite  coal  there  is  no  sensible  loss  under  a  tem- 
perature of  700°  Fahr." 

W.  K. 

APPENDIX  XII. 

PROXIMATE   ANALYSES   OF    COAL. 

For  comparing  the  proximate  analyses  of  different  coals  it  is  desir- 
able that  they  should  be  reported  in  a  uniform  style,  The  four  con- 
stituents determined  by  heating  in  a  crucible  should  be  given,  and 
their  sum  should  equal  100  per  cent.  When  sulphur  is  determined  it 
should  be  stated  separately,  and  it  should  not  be  subtracted  from  the 
fixed  carbon  and  the  volatile  matter  (half  from  each  as  is  the  custom  of 
some  chemists,  or  0.4  from  one  and  0.6  from  the  other,  as  is  the  custom 
of  others),  since  it  cannot  be  known  what  proportion  of  sulphur  escapes 
from  the  crucible  with  the  volatile  matter  and  what  proportion  is  burned 
with  the  fixed  carbon.  The  carbon  ratio,  that  is,  the  ratio  of  fixed  car- 
bon to  volatile  matter,  should  also  be  stated,  preferably  as  percentages 

*For  scientific  investigations  in  which  extreme  accuracy  is  desired,  the 
author  would  suggest  that  the  coal  be  dried  in  an  atmosphere  of  nitrogen,  to 
avoid  oxidation,  and  that  the  moisture  driven  off  be  absorbed  by  chloride  of  cal- 
cium and  weighed.  The  loss  of  weight  by  the  coal  should  equal  the  gain  of  weight 
by  the  chloride  of  calcium  if  no  volatile  matter  is  driven  off. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  353 

of  their  sum,  thus:  40  per  cent  volatile  matter,  60  per  cent  fixed  car- 
bon, which  is  equivalent  to  a  carbon  ratio  of  1^. 

The  proximate  analysis  is  a  most  valuable  means  of  identifying  the 
general  character  of  the  coal.  First,  the  amount  of  volatile  matter, 
expressed  as  a  percentage  of  the  combustible,  distinguishes  between 
the  anthracite,  the  semi-bituminous,  and  the  bituminous  coals.  Second, 
among  the  bituminous  coals  the  moisture  is  an  important  guide  to  the 
character  of  the  coal.  Third,  the  ash  is  also  a  criterion  of  the  coal's 
value.  Fourth,  the  sulphur  taken  in  connection  with  the  ash  is  also 
an  indication  of  the  value  of  the  fuel,  as  high  sulphur  generally  is 
found  in  a  coal  which  clinkers  badly,  and  with  which  it  is  difficult  to 
obtain  the  rated  capacity  of  a  boiler. 

W.  K. 

APPENDIX  XV. 

DETERMINATION   OF   THE   MOISTURE   IN   THE    STEAM. 

The  throttling  steam  calorimeter,  first  described  by  Professor  Pea- 
body  in  the  Transactions  vol.  x.  page  327,  and  its  modifications  by 
Mr.  Barrus,  vol.  xi.  page  790;  vol.  xvii.  page  617;  and  by  Professor 
Carpenter,  vol.  xii.  page  840 ;  also  the  separating  calorimeter  designed 
by  Professor  Carpenter,  vol.  xvii.  page  608  ;  which  instruments  are 
used  to  determine  the  moisture  existing  in  a  small  sample  of  steam 
taken  from  the  steam-pipe,  give  results,  when  properly  handled,  which 
may  be  accepted  as  accurate  within  0.5  per  cent  (this  percentage 
being  computed  on  the  total  quantity  of  the  steam)  for  the  sample 
taken.  The  possible  error  of  0.5  per  cent  is  the  aggregate  of  the 
probable  error  of  careful  observation,  and  of  the  errors  due  to  inaccur- 
acy of  the  pressure-gauges  and  thermometers,  to  radiation,  and,  in  the 
case  of  the  throttling-calorimeter,  to  the  possible  inaccuracy  of  the 
figure  0.48  for  the  specific  heat  of  superheated  steam,  which  is  used 
in  computing  the  results.  It  is,  however,  by  no  means  certain  that 
the  sample  represents  the  average  quality  of  the  steam  in  the  pipe 
from  which  the  sample  is  taken.  The  practical  impossibility  of  ob- 
taining an  accurate  sample,  especially  when  the  percentage  of  moist- 
ure exceeds  two  or  three  per  cent,  is  shown  in  the  two  papers  by  Pro- 
fessor Jacobus  in  Transactions,  vol.  xvi.  pages  448,  1017. 

In  trials  of  the  ordinary  forms  of  horizontal  shell  and  of  water- 
tube  boilers,  in  which  there  is  a  large  disengaging  surface,  when  the 
water-level  is  carried  at  least  10  inches  below  the  level  of  the  steam 
outlet,  and  when  the  water  is  not  of  a  character  to  cause  foaming,  and 
when  in  the  case  of  water-tube  boilers  the  steam  outlet  is  placed  in  the 
rear  of  the  middle  of  the  length  of  the  water-drum,  the  maximum- 
quantity  of  moisture  in  the  steam  rarely,  if  ever,  exceeds  two  per  cent; 
and  in  such  cases  a  sample  taken  with  the  precautions  specified  in 
Article  XII/.  of  the  Code  may  be  considered  to  be  an  accurate  average 
sample  of  the  steam  furnished  by  the  boiler,  and  its  percentage  of 
moisture  as  determined  by  the  throttling  or  separating  calorimeter 


354  STEAM-BOILER  ECONOMY. 

may  be  considered  as  accurate  within  one-half  of  one  per  cent.  For 
scientific  research,  and  in  all  cases  in  which  there  is  reason  to  suspect 
that  the  moisture  may  exceed  two  per  cent,  a  steam  separator  should 
be  placed  in  the  steam  -pipe,  as  near  to  the  steam  outlet  of  the  boiler 
as  convenient,  well  covered  with  felting,  all  the  steam  made  by  the 
boiler  passing  through  it,  and  all  the  moisture  caught  by  it  carefully 
weighed  after  being  cooled.  A  convenient  method  of  obtaining  the 
weight  of  the  drip  from  the  separator  is  to  discharge  it  through  a  trap 
into  a  barrel  of  cold  water  standing  on  a  platform  scale.  A  throttling 
or  a  separating  calorimeter  should  be  placed  in  the  steam-pipe,  just 
beyond  the  steam  separator,  for  the  purpose  of  determining,  by  the 
.sampling  method,  the  small  percentage  of  moisture  which  may  still  be 
in  the  steam  after  passing  through  the  separator. 

The  formula  for  calculating  the  percentage  of  moisture  when  the 
throttling  calorimeter  is  used  is  the  following: 


in  which  w  =  percentage  of  moisture  in  the  steam,  H=  total  heat, 
and  L  =  latent  heat  per  pound  of  steam  at  the  pressure  in  the  steam- 
pipe,  h  =  total  heat  per  pound  of  steam  at  the  pressure  in  the  dis- 
charge side  of  the  calorimeter,  Jc  =  specific  heat  of  superheated  steam, 
T  =  temperature  of  the  throttled  and  superheated  steam  in  the  calo- 
rimeter, and  t  =  temperature  due  to  the  pressure  in  the  discharge  side 
of  the  calorimeter,  =  212°  Fahr.,  at  atmospheric  pressure.  Taking 
k  =  0.48  and  t  =  212,  the  formula  reduces  to 

«  =  100  x  H~  1146'6~ 


W.  K. 

APPENDIX  XVI. 

CORRECTION  FOR  RADIATION  FROM  THROTTLING  CALORIMETERS. 

The  formulae  usually  given  for  determining  moisture  in  a  throt- 
tling calorimeter,  including  that  given  above  by  Mr.  Kent,  makes  no 
allowance  for  radiation  from  the  exterior  surfaces  of  the  instrument.  It 
is  true  that  this  allowance  is  small  and  does  not  affect  the  results  but 
a  small  fraction  of  1  per  cent;  but  it  nevertheless  exists,  and  should 
properly  be  taken  into  account.  In  my  own  work  I  have  found  that 
the  radiation  reduces  the  temperature  of  the  wire-drawn  steam  some  six 
degrees,  and  this  represents  about  0.3  of  1  per  cent  of  moisture.  My 
practice  is  to  allow  for  the  radiation  by  determining  the  normal  for 
the  instrument,  as  described  in  Appendix  XVII. 

It  should  be  noted  here  that  this  normal  can  be  readily  determined 
when  the  calorimeter  is  attached  to  a  horizontal  section  of  the  steam- 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


355 


pipe,  and  the  condensing  surface  immediately  above  the  sampling-pipe 
is  thus  reduced  to  a  minimum. 

G.  H.  B. 

APPENDIX   XVII. 

COMBINED  CALORIMETER  AND  SEPARATOR. 

The  form  of  steam  calorimeter  which  the  writer  uses  is  termed 
the  "1895  pattern  "  universal  steam  calorimeter,  and  is  a  modification 
of  the  one  described  in  the  Transactions,  vol.  xi.  page  790.  It  is  illus- 
trated in  the  accompanying  cut,  Fig.  Ill,  which  is  reprinted  from  page 
(US,  vol.  xvii.  in  the  Trans- 
actions. It  consists  of  a  throt- 
tling calorimeter  and  separa- 
tor combined,  the  latter  being 
attached  to  the  outlet  where 
the  steam  of  atmospheric  pres- 
sure is  escaping.  If  the 
moisture  is  too  great  to  be  de- 
termined by  the  readings  of 
the  two  thermometers,  the 
separator  catches  the  balance, 
and  the  total  quantity  of 
moisture  is  made  up  in  part  of 
that  shown  by  the  thermome- 
ters, and  in  part  of  that  col- 
lected from  the  separator.  The 
percentage  of  moisture  shown 
by  the  thermometers  is  ob-  FIG.  111.— STEAM  CALORIMETER. 
tained  by  referring  the  indication  of  the  lower  thermometer  to  the  nor- 
mal reading  of  that  thermometer  with  dry  steam,  and  dividing  the  fall 
of  temperature  by  the  constant  of  the  instrument  for  one  per  cent  of 
moisture.  The  normal  reading  is  determined  by  observing  the  indi- 
cations when  steam  in  the  main  pipe  is  in  a  quiescent  state,  and  the 
constant  is  a  quantity  varying  from  21°  at  80  pounds  pressure  to  20° 
at  200  pounds  pressure.  The  percentage  of  moisture,  if  any,  dis- 
charged from  the  separator,  is  found  by  dividing  its  quantity  corrected 

radiation  by  the  total  quantity  of  steam  and  water  passing  through 
the  instrument  in  the  same  time,  as  ascertained  by  experiment,  and 
multiplying  the  result  by  100. 

G.  H.  B. 

APPENDIX   XVIII. 

CORRECTIONS    FOR    QUALITY    OF    STEAM. 

Given  the  percentage  of  moisture  or  number  of  degrees  of  super- 
heating, it  is  desirable  to  develop  formulae  showing  what  we  have 
termed  "  the  factor  of  correction  for  quality  of  steam,"  or  the  factor 


356  STEAM-BOILER  ECONOMY. 

by  which  the  "  apparent  evaporation  "  determined  by  a  boilej-test  is 
to  be  multiplied  to  obtain  the  "  evaporation  corrected  for  quality  of 
steam."  It  has  been  customary  to  call  the  proportional  weight  of 
steam  in  a  mixture  of  steam  and  water  "  the  quality  of  the  steam," 
and  it  is  not  desirable  to  change  this  designation.  The  same  term 
applies  when  the  steam  is  superheated,  by  employing  the  "  equivalent 
evaporation,"  or  that  obtained  by  adding  to  the  actual  evaporation 
the  proportional  weight  of  water  which  the  thermal  value  of  the 
superheating  would  evaporate  into  dry  steam  from  and  at  the  tem- 
perature due  to  the  pressure.  "  The  factor  of  correction  for  quality 
of  steam"  in  a  boiler-test  diff  era  from  the  "  quality  "  itself,  from  the 
fact  that  the  temperature  of  the  feed-water  is  lower  than  that  of  the 
steam. 

Let  Q  =  quality  of  moist  steam  as  described  above; 

Ql  =  the  quality  of  superheated  steam  as  described  above; 

P  =  the  proportion  of  moisture  in  the  steam; 

Tc  —  the  number  of  degrees  of  superheating; 

F  =  the  factor  of  correction   for  the  quality  of  the  steam 
when  the  steam  is  moist; 

Fl  =  the  factor  of  correction  for   the  quality  of   the  steam 
when  the  steam  is  superheated; 

H  =  the  total  heat  of  the  steam  due  to  the  steam-pressure  ; 

L  =  the  latent  heat  of  the  steam  due  to  the  steam-pressure; 

T  =  the  temperature  of  the  steam  due  to  the  steam-pressure; 

TI  =  the  total  heat  in  the  water  at  the  temperature  due  to 
the  steam-pressure  ;  * 

/  =  the  temperature  of  the  feed-water; 

Jj  =  the  total  heat  in  the  feed-water  due  to  the  temperature.* 
Therefore,  for  moist  steam  : 


P  =  i-  Q,  .    '.    .    .    «    ,    .    .    (2) 
Q  +  P  =  i  .....    •    -    .    -    (3) 

See  also  equation  (6). 

"With  both  the  condensing  and  throttling  calorimeters  the  water 
and  steam  are  withdrawn  from  the  boiler  at  the  temperature  of  the 
steam,  and  with  a  separator  the  water  can  only  be  accurately  measured 
when  under  pressure,  so  that  the  difference  between  the  steam  and 
the  moisture  in  the  steam,  as  they  leave  the  boiler,  is  simply  that  the 
former  has  received  the  latent  heat  due  to  the  pressure  and  the  latter 
has  not.  There  is,  however,  imparted  to  the  water  in  the  boiler,  not 

*  Most  tables  of  the  properties  of  steam  and  of  water  are  based  on  the  total 
heat  of  steam  and  water  above  32  degrees  Fahr.  For  such  tables  the  total  heat 
in  the  water  at  a  given  temperature  is  equal  approximately  to  the  corresponding 
temperature  minus  32  degrees.  Exact  values  should,  however,  be  taken  from 
the  tables. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  o5T 

only  the  latent  heat  in  the  portion  evaporated,  but  the  sensible  heat 
due  to  raising  the  temperature  of  all  the  water  from  that  of  the  feed- 
water  to  that  of  the  steam  due  to  the  pressure. 

In  equation  (3)  the  proportional  part  Q  receives  from  the  boiler 
both  the  sensible  and  the  latent  heat,  or  the  total  heat  above  the 
temperature  of  the  feed  =  Q(H —  «/",)  thermal  units,  and  the  part  P 
the  difference  in  sensible  heat  between  the  temperatures  of  the  steam 
and  of  the  feed-water  =  P(Tl  —  JJ  thermal  units.  If  all  the  water 
were  evaporated,  each  pound  would  receive  the  total  heat  in  the  steam 
above  the  temperature  of  the  feed,  or  H  —  Jr  "  The  factor  of  cor- 
rection for  the  quality  of  the  steam,"  when  there  is  no  superheating, 
is  therefore 


777    "OV"*--*- J  \)  •*•     y-*    1  ^  I/        /}        I          p[    "*•  1 

7TT  ~      Hj     ~T    •*     V    ET 

/I    —   t/J  \-tz    —  t 

The  superheating  of  the  steam. requires  0.48  of  a  thermal  unit. for 
each  degree  the  temperature  of  the  steam  is  raised,  so  for  Ic  degrees 
of  superheating  there  will  be  0.48&  thermal  units  per  pound  weight 
of  steam  and  the  "  factor  of  correction  for  the  quality  of  the  steam  " 
with  superheating. 


_,l          ._  0.48ft 

H  -  j^  h  H  -  /; 

See  also  equation  (7). 

With  the  throttling  calorimeter  the  percentage  of  moisture  P,  or 
number  of  degrees  of  superheating,  are  determined  as  explained  in 
Appendices  XV  and  XVI. 

Since  the  invention  of  the  throttling  calorimeter  (Appendix  XV) 
the  use  of  the  original  condensing,  or  so-called  barrel,  calorimeter  is 
no  longer  warranted.  Accurate  results  should,  however,  be  obtained 
by  condensing  all  the  steam  generated  in  the  boiler  and  this  plan  has 
been  followed  in  certain  cases.  It  has,  therefore,  been  thought  desir- 
able to  add  other  formulae  applicable  to  condensing  calorimeters. 
The  following  additional  notation  is  required: 
W  —  the  original  weight  of  the  water  in  calorimeter,  or  weight  of 

circulating  water  for  a  surface-condenser; 

•w  =  the  weight  of  water  added  to  the  calorimeter  by  blowing  steam 
into  the  water,  or  of  "  water  of  condensation  "  with  a  surface- 
condenser; 
t  —  total  heat   of  water   corresponding  to    initial  temperature    of 

water  in  calorimeter; 
^  —  total    heat    of   water    corresponding   to    final    temperature    in 

calorimeter; 
Evidently,  then : 

W  (tl  —  t)  =  the  total  thermal  units  withdrawn  from  the  boiler  and 
imparted  to  the  water  in  calorimeter; 


358  STEAM-BOILER  ECONOMY. 

'  —  Ci  ~  0  —  ^ie  thermal  units  per  pound  of  water  withdrawn  from 

the  boiler  and  imparted  to  the  water  in  calorimeter,  from  which 
should  be  deducted  Tv  —  ^  to  obtain  the  number  of  thermal 
units  per  pound  of  water  withdrawn  from  the  boiler  at  the 
pressure  due  to  the  temperature  T. 

Since  only  the  latent  heat  L  is  imparted  to  the  portion  of  the 
•water  evaporated,  the  quality  Q,  or  proportional  quantity  evaporated, 
may  be  obtained  by  dividing  the  total  thermal  units  per  pound  of 
water  abstracted  at  the  pressure  due  to  the  temperature  T  by  the 
latent  heat  L.  Hence, 

•     •     •     (6) 

The  value  Q  applies  when  the  second  term  is  less  than  unity;  P 
may  be  derived  therefrom  by  substitution  in  equation  (2)  and  F  from 
equation  (4). 

Ql  applies  when  the  second  term  of  the  above  equation  is  greater 
than  unity,  which  shows  that  the  steam  is  superheated,  and,  as  in  this 
case,  the  heating  value  of  the  superheat  has  already  been  measured 
by  heating  the  water  of  the  calorimeter;  the  proportional  thermal 
value  of  the  same,  in  terms  of  the  latent  heat  L,  is  represented 
directly  by  Qr  —  1,  and  we  have  as  the  factor  of  correction  for  the 
quality  of  the  steam  with  superheating: 


l  l_  ,  - 

?*  ~H'-  j,  H-J,  ••  ; 

See  also  equation  (5). 

When  the  quality  is  greater  than  1,  or  equals  Ql9  the  number  of 
degrees  of  superheating: 


C.  E.  E. 

APPENDIX  XIX. 

THE    QUALITY    OF    SUPERHEATED    STEAM. 

The  quality  of  the  superheated  steam  is   determined  from   the 
number  of  degrees  of  superheating  by  using  the  following  formula  : 


in  which  L  is  the  latent  heat  in  British  thermal  units  in  one  pound 
of  steam  of  the  observed  pressure  ;   T  the  observed  temperature,  and 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  359 

t  the  normal  temperature  due  to  the  pressure.  This  normal  tempera- 
ture should  be  determined  by  obtaining  a  reading  of  the  thermometer 
when  the  fires  are  in  a  dead  condition  and  the  superheat  has  dis- 
appeared; this  temperature  being  observed  when  the  pressure  as 
shown  by  the  gauge  is  the  average  of  the  readings  taken  during  the 
trial.  Observations  being  made  by  the  same  instrument,  errors  of 
gauge  or  thermometer  are  practically  eliminated. 

G.  H.  B. 

APPENDIX  XX. 

EFFICIENCY    OF   THE   BOILEE. 

The  efficiency  of  the  boiler,  not  including  the  grate  (or  the 
efficiency  based  upon  combustible)  is  a  more  accurate  measure  of 
comparison  of  different  boilers  than  the  efficiency  including  the  grate 
(or  the  efficiency  based  upon  coal);  for  the  latter  is  subject  to  a 
number  of  variable  conditions,  such  as  size  and  character  of  the  coal, 
air-spaces  between  the  grate-bars,  skill  of  the  fireman  in  saving  coal 
from  falling  through  the  grate,  etc.  It  is,  moreover,  subject  to  errors 
of  sampling  the  coal  for  drying  and  for  analysis,  which  affect  the 
result  to  a  greater  degree  than  they  do  the  efficiency  based  upon  com- 
bustible, for  the  reason  that  the  heating  value  per  pound  of  combusti- 
ble of  any  sample  selected  from  a  given  lot,  such  as  a  car-load,  of  coal 
is  practically  a  constant  quantity  and  is  independent  of  the  percentage 
of  moisture  and  ash  in  the  sample ;  while  the  sample  itself,  upon  the 
heating  value  of  which  the  efficiency  based  on  coal  is  calculated,  may 
differ  in  its  percentage  of  moisture  and  ash  from  the  average  coal 
used  in  the  boiler-test. 

When  the  object  of  a  boiler-test  is  to  determine  its  efficiency  as 
an  absorber  of  heat,  or  to  compare  it  with  other  boilers,  the  efficiency 
based  on  combustible  is  the  one  which  should  be  used;  but  when  the 
object  of  the  test  is  to  determine  the  efficiency  of  the  combination  of 
the  boiler,  the  furnace,  and  the  grate,  the  efficiency  based  on  coal 
must  necessarily  be  used. 

w.  K. 

APPENDIX  XXI. 

DISTRIBUTION    OF    THE    HEATING    VALUE    OF    THE    FUEL. 

In  the  operation  of  a  steam-boiler  the  following  distribution  of  the 
total  heating  value  of  the  fuel  takes  place : 

1.  Loss  of  coal  or  coke  through  the  grate. 

2.  Ilnburned  coal  or  coke  carried  in  the  shape  of  dust  or  sparks 
beyond  the  bridge-wall. 

3.  Heating  to  212°  the  moisture  in  the  coal,  evaporating  it  at  that 
temperature,  and  evaporating  the  steam  made  from  it  to  the  tem- 
perature  of   the   flue-gases,  =  weight   of   the   moisture   in   pounds 
X  [(212°  -  t)  +  966  +  OA8(T  -  212)],  in  which  T  is  the  tempera- 


360  STEAM-BOILER  ECONOMY. 

ture  (Fahr.)  of  the  flue-gases  and  t  the  temperature  of  the  external 
air. 

4.  Loss  of  heat  due  to  steam  which  is  formed  by  burning  the 
hydrogen  contained  in  the  coal,  and  which  passes  into  the  chimney 
as   superheated   steam,    =   9    times    the   weight    of   the    hydrogen 
X  [(212  -  t)  +  966  -t-  0.48(T  -  212)]. 

5.  Superheating  the  moisture  in  the  air  supplied  to  the  furnace 
to   the   temperature   of   the   flue-gases,  =  weight    of   the   moisture 
X  QAS(T—  t). 

6.  Heating  of  the  gaseous  products  of  combustion  (not  including 
steam)  to  the  temperature  of  the  flue,  =  their  weight  x  0.24(77  —  t). 
1      7.  Loss  due  to  imperfect  burning  of  the  carbon  of  the  coal  and  to 
non-burning  of  the  volatile  gases. 

8.  Radiation  from  the  boiler  and  furnace. 

9.  Heat  absorbed  by  the  boiler,  or  useful  work. 

Item  1  depends  upon  the  size  of  the  spaces  between  the  grate- 
bars  ;  upon  the  kind  of  grate,  as  a  plain,  shaking,  or  travelling  grate ; 
upon  the  size  of  the  coal;  upon  the  character  of  the  coal,  as  it 
requires  to  be  more  or  less  distributed  on  the  grate  in  order  to  get  a 
sufficient  supply  of  air  through  it;  upon  the  rate  of  driving  of  the 
furnace,  rapid  driving  with  some  coals  requiring  more  frequent  shak- 
ing or  cleaning  of  the  grate  than  slow  driving;  and  upon  the  skill  of 
the  fireman. 

Item  2  depends  upon  the  nature  and  fineness  of  the  coal  and  upor 
the  force  of  the  draft.  It  is  usually  so  small  as  to  be  inappreciable 
in  its  effect  upon  the  results  of  the  trial  of  a  stationary  boiler  driven 
with  natural  draft,  but  in  locomotives,  with  rapid  rates  of  combus- 
tion, it  often  becomes  quite  important. 

Item  3  depends  upon  the  amount  of  moisture  in  the  coal. 

Item  4  depends  upon  the  amount  of  hydrogen  in  the  coal. 

Item  5  depends  upon  the  amount  of  moisture  in  the  air.  The 
moisture  in  the  air  may  be  obtained  from  its  temperature  and  relative 
humidity,  as  determined  by  a  wet-and-dry-bulb  thermometer,  by 
reference  to  hygrometric  tables.  The  loss  of  heat  due  to  the  moisture 
in  the  air  will  rarely  exceed  0.25  per  cent  of  the  heating  value  of  the 
fuel,  and  it  may  usually,  therefore,  be  neglected. 

Item  6  depends  chiefly  upon  the  type  and  proportions  of  the 
boiler,  and  upon  the  rate  at  which  it  is  driven.  This  item  is  usually 
the  largest  of  all  the  heat-losses. 

Items  3,  4,  5,  and  6  depend  also  on  the  temperature  of  the  flue- 
gases. 

Item  7  depends  upon  the  character  of  the  coal  and  of  the  furnace, 
and  upon  the  skill  of  the  firemen.  This  loss  may  be  very  large,  20 
per  cent  or  more  of  the  heating  value  of  the  coal,  when  highly 
bituminous  coals  are  used  in  a  furnace  not  adapted  to  them. 

Item  8  depends  chiefly  upon  the  type,  size,  and  setting  of  the 
boiler,  and,  when  expressed  as  a  percentage  of  the  total  heat  of  the 
fuel,  upon  the  rate  at  which  it  is  driven. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  361 

Item  9  is  the  heat  absorbed  by  the  boiler,  or  the  useful  work.  It 
is  also  the  difference  between  the  total  heating  value  of  the  coal  and 
the  sum  of  the  losses  of  items  1  to  8  inclusive. 

w.  K. 

APPENDIX  XXV. 

DISCREPANCY   BETWEEN    COMMERCIAL   AND    EXPERIMENTAL   RESULTS. 

The  final  result  sought  by  manufacturers,  in  initiating  tests  of 
steam  or  other  machinery  in  actual  use,  is  the  value  of  the  work,  done 
measured  in  dollars  and  cents.  In  some  cases  the  broad  question  is 
raised  as  to  the  saving  that  may  be  accomplished  by  installing 
improved  boilers,  engines,  or  other  machinery;  but  more  generally  it 
is  desired  to  ascertain  what  can  be  done  to  produce  saving  with  the 
apparatus  already  in  place  under  the  actual  conditions  that  prevail  at 
the  particular  location.  In  both  these  cases  it  is  necessary  to  ascer- 
tain the  average  cost  of  the  work  done  commercially  previous  to  the 
test.  Frequently,  in  fact  generally,  this  important  fact  will  not  be 
ascertained  by  an  elaborate  trial,  for  the  reason  that  everything  will 
be  put  in  order  for  the  test,  and  all  details  of  the  trial  be  conducted 
so  carefully  that  the  losses  due  to  average  carelessness  or  want  of  skill 
in  the  past  will  be  eliminated,  the  engineer  making  the  test  will  not 
receive  proper  credit,  and  the  owners  on  seeing  the  report  may  con- 
clude that  they  are  already  doing  very  well,  and  perhaps  continue  old 
methods  with  fancied  security.  If  the  cost  of  the  output  of  the  fac- 
tory for  a  given  time  were  ascertained  in  terms  of  the  coal  burned 
during  the  same  time,  and  compared  with  the  corresponding  cost  for 
the  time  of  the  trial,  the  latter  would  frequently  be  found  to  be  one- 
eighth  to  one-third  less  than  the  former,  and  it  might  not  be  possible 
to  tell  what  had  caused  the  difference;  for  instance,  whether  it  was 
due  to  putting  in  order  the  machinery  prior  to  the  tests,  to  greater 
care  exercised  by  the  fireman  under  the  spur  of  careful  watching,  or 
whether,  as  is  usually  claimed,  the  coal  was  different,  etc.,  etc.  The 
losses  are  generally  due  in  the  main  to  the  carelessness  of  the  firemen. 
It  follows,  therefore,  that  the  cost  of  the  power  under  average  condi- 
tions must  be  obtained  in  some  quiet  way  preliminarily.  Frequently 
the  comparison  of  the  output  of  the  factory  with  the  coal  burned  will 
not  be  sufficiently  accurate,  and  it  will  be  necessary  to  devise  some 
corresponding  check  which  will  not  interfere  with  the  regular  routine 
of  the  establishment.  The  work  of  the  boilers  may  be  checked  by 
arranging  a  meter  so  as  to  continuously  measure  the  feed-water;  and 
its  record,  compared  with  the  total  weight  of  coal  purchased,  will  fre- 
quently give  the  check  desired.  Such  a  check  becomes  more  difficult 
when  it  is  desirable  to  ascertain  the  performances  of  particular 
boilers,  and  the  coal-supply  is  common  to  all  boilers ;  but  by  assigning 
particular  weighed  car-loads  of  coal  to  the  particular  boilers,  without 
any  intimation  to  the  firemen  that  they  are  being  watched,  it  may  be 
possible  to  ascertain  the  average  performance  of  the  boilers  used  for 


362 


STEAM-BOILER  ECONOMY. 


the  particular  purpose.  Preliminary  experiments  of  this  kind  con- 
ducted without  notice  to  employes,  and  continued  through  a  long 
period,  will  furnish  a  basis  for  comparison  with  elaborate  tests,  and  it 
will  then  be  possible  to  point  out  clearly  where  the  several  losses  have 
taken  place,  and  the  testing  engineer  will  get  the  credit  for  the  saving 
shown. 


c.  E.  E. 


APPENDIX  XXVI. 

RECORDING    STEAM-GAUGE. 


A    good    recording    steam-gauge,    Edson's    or    other,    carefully 
adjusted,  should  be  used  and  accurately  compared  with  the  steam- 


FIG.  112. — U-TUBE  DRAFT-GAUGE,     FIG.  113. — BARRUS'S  DRAFT-GAUGE,  WITH 
HALF  SIZE.  MAGNIFIED  READINGS. 

gauge  at  stated  intervals.    Such  an  automatic  record,  nicely  integrated, 
is  a  good  check  on  the  record  of  the  steam-gauges. 

J.  c.  H. 


APPENDIX  XXIX. 

DRAFT-GAUGE. 


The  ordinary  form  of  draft-gauge,  consisting  of  the  IT  tube  (Fig. 
112),  containing  water,  lacks  sensitiveness  when  used  for  measuring 
small  quantities  of  draft.  An  instrument  which  the  writer  has  used 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


363 


satisfactorily  for  a  number  of  years  multiplies  the  ordinary  indications 
as  many  times  as  desired.  It  consists  of  a  U  tube  made  of  ^-in.  glass, 
surmounted  by  two  larger  tubes,  or  chambers,  having  a  diameter  of 
2£  ins.,  as  shown  in  Fig.  113.  Two  different  liquids  which  will  not 
mix,  and  which  are  of  different  color,  are  used,  one  occupying  the 
portion  AB,  and  the  other  the  portion  BCD.  The  movement  of  the 
line  of  demarcation  is  proportional  to  the  difference  in  the  areas  of 
the  chambers  and  of  the  U  tube  below.  The  liquids  generally 
employed  are  alcohol  colored  red  and  a  certain  grade  of  lubricating 
oil.  A  multiplication  varying  from  eight  to  ten  times  is  obtained 
under  these  circumstances;  in  other  words,  with  ^-in.  draft  the  move- 
ment of  the  line  of  demarcation  is  some  2  ins. 

The   instrument   is   calibrated  by  referring   it   to   the   ordinary 
U-tube  gauge. 

G.  H.  B. 


I 


5" >. 

A 


APPENDIX  XXX. 

DRAFT-GAUGE. 

The  accompanying  sketch  (Fig.  114)  represents  a  very  sensitive 
and  accurate  draft-gauge  recently  constructed  by  the  writer.  A  light 
cylindrical  tin  can  A,  5  ins.  diameter  and 
6  ins.  high,  is  inverted  and  suspended  inside 
of  a  can  B,  6  ins.  diameter,  6  ins.  high,  by 
means  of  a  long  helical  spring.  Inside  of 
the  larger  can  a  ^-in.  tube  is  placed,  with 
one  end  just  below  the  level  of  the  upper 
edge,  while  the  other  end  passes  through  a 
hole  cut  in  the  side  of  the  can,  close  to  the 
bottom,  solder  being  run  around  the  tube  so 
as  to  close  the  hole  and  make  the  can  water- 
tight. The  can  is  filled  with  water  to  within 
about  half  an  inch  of  the  top,  and  the  inner 
can  is  suspended  by  the  spring  so  that  its 
lower  edge  dips  into  the  water,  the  height  of 
the  support  of  the  spring  being  adjusted 
accordingly. 

The  small  tube  being  open  at  both  ends, 
the  air  enclosed  in  the  can  A  is  at  atmos- 
pheric pressure,  and  the  spring  is  extended 
by  the  weight  of  the  can.  The  end  of  the 
tube  which  projects  from  the  bottom  of  the 
can  being  now  connected  by  means  of  a 
rubber  tube  with  a  tube  leading  into  the  flue,  or  other  chamber,  whose 
draft  or  suction  is  to  be  measured,  air  is  drawn  out  of  the  can  A  until 
the  pressure  of  the  remaining  air  is  the  same  as  that  of  the  flue.  The 
external  atmosphere  pressing  on  the  top  of  the  can  A  causes  it  to  sink 
deeper  in  the  water,  extending  the  spring  until  its  increased  tension 


H - 8--~ >} 

FIG.  114. — DRAFT-GAUGE 
FOR  LIGHT  PRESSURES. 


364  STEAM-BOILEE  ECONOMY. 

just  balances  the  difference  of  the  opposing  vertical  pressures  of  the 
air  inside  and  outside  of  the  can.  The  product  of  this  difference  in 
pressure,  expressed  as  a  decimal  fraction  of  a  pound  per  square  inch, 
multiplied  by  the  internal  area  of  the  can  in  square  inches,  equals  the 
tension  of  the  spring  (above  that  due  to  the  weight  of  the  can)  in 
pounds  or  fraction  of  a  pound.  The  extension  of  a  helical  spring 
being  proportional  to  the  force  applied,  the  distance  travelled  down- 
ward by  the  can  A  measures  the  force  of  suction,  that  is,  the  draft. 
The  movement  of  the  can  may  conveniently  be  measured  by  having  a 
celluloid  scale  graduated  to  50ths  of  an  inch  fastened  to  the  side  of 
the  can  A,  and  a  fine  pointer  fixed  to  the  upper  edge  of  the  can  B, 
almost  touching  the  scale. 

To  reduce  the  readings  of  the  scale  to  their  equivalents  in  inches 
of  water-column,  as  read  on  the  ordinary  U-tube  gauge,  we  have  the 
following  formulae  : 

Let  P  =  force  in  pounds  required  to  stretch  the  spring  1  in.  ; 

E  =  elongation  of  the  spring  in  inches  ; 

A  —  area  of  the  inner  can  in  square  inches; 

d  =  difference  in  pressure  or  force  of  the  draft  in  pounds  per 
square  inch; 

D  —  difference  in  pressure  in  inches  of  water  =  2 

A  D 

Ad  =  ~i  =  0.0361.4A 

27.71.flP 
~A~ 

0.03G1AD 


The  last  equation  shows  that  for  a  constant  force  of  draft  the 
elongation  of  the  spring  or  the  movement  of  the  can  may  be  increased 
by  increasing  the  area  of  the  can  or  by  decreasing  the  strength  of  the 
spring.  The  strength  of  the  spring  may  be  increased,  that  is,  its 
sensitiveness  may  be  decreased,  by  increasing  either  its  length  or  the 
diameter  of  the  helix,  or  by  decreasing  the  diameter  of  the  wire  of 
which  it  is  made.  We  thus  have  at  command  the  means  of  making 
the  apparatus  of  any  desired  degree  of  sensitiveness. 

Applying  the  above  formulae,  let  it  be  required  to  determine  the 
movement  of  the  can  corresponding  to  a  draft  of  1  in.  of  water- 
column,  the  can  A  having  a  diameter  of  5  ins.  =  19.63  ins.  area,  and 
the  spring  of  such  a  strength  that  0.1  Ib.  elongates  it  1  in.  Here 
P  =  0.1;  A  =  19.63;  D  =  1. 

„       0.0361  X  19.63 

E  —  -  -  —  7.09  inches. 

That  is,  the  instrument  multiplies  the  readings  of  the  U  tube  7.09 
times.  The  precision  of  the  instrument  is,  however,  far  greater  than 
this  figure  would  indicate;  for  in  the  U  tube  it  is  exceedingly  difficult 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


365 


to  read  with  precision  the  difference  in  height  of  the  two  menisci, 
while  with  this  apparatus  readings  in  the  scale  may  easily  be  made  to 
-fa  in.,  which,  with  the  multiplication  of  7,  is  equivalent  to  ^J?  of  an 
inch  of  water-column.  The  instrument  may  also  be  calibrated  by 
directly  comparing  its  readings  with  those  of  an  ordinary  U-tube 
gauge. 

W.  K. 

APPENDIX  XXXI. 

SAMPLING    FLUE-GASES. 

Very  great  diversities  in  the  composition  of  flue-gases  often  exist 
in  the  same  flue  at  the  same  time.  To  obtain  a  fair  sample,  it  has 
been  found  sufficient  to  have 
one  orifice  to  draw  off  gases 
through  for  each  25  sq.  ins.  of 
cross-section  of  flue.  The 
pipes  must  be  of  equal  diameter 
and  of  equal  length.  One- 
quarter-in.  gas-pipes,  all  alike 
at  the  ends,  and  of  equal 
lengths,  answer  well.  Similar 
steel  tubes  will  be  still  better 
(because  smoother  and  more 
uniform).  These  should  be 
secured  in  a  box  or  block  of 
galvanized  sheet  iron,  equal  in 
thickness  to  one  course  of 
brick,  in  such  a  manner  that 
the  open  ends  may  be  evenly 
distributed  over  the  area  of  the 
flue  A  (Fig.  115),  and  their 
other  open  ends  enclosed  in 

the    receiver  B.     If  the  flue-  FIG.  115.— METHOD  OF  SAMPLING 

gases  be  drawn  off   from  the  FLUE-GASES. 

receiver  B  by  four  tubes,  CC,  into  a  mixing-box  D  beneath,  about 
3-in.  cube,  a  good  mixture  can  be  obtained.  Two  such  "  samplers/' 
one  above  the  other  a  foot  apart,  in  the  same  flue,  will  furnish  samples 
of  gases  which  show  by  analysis  the  same  composition. 

j.  c.  H. 


366  STEAM-BOILER  ECONOMY. 

APPENDIX  XXXIII. 

THE   OKSAT   APPARATUS   FOR   ANALYZING    FLUE-GASES.* 

The  writer  has  made  extensive  use  of  the  Orsat  apparatus  in  his 
boiler-testing,  and  has  found  the  work  not  only  interesting,  but 
exceedingly  instructive  and  valuable.  Its  chief  value  lies  in  the  guide 
which  it  affords  in  determining  what  kind  of  firing  is  most  advan- 
tageous where  the  fuel  is  bituminous  coal.  In  applying  the  results 
of  analyses  to  working  out  the  heat-balance  of  a  boiler-test,  the 
writer's  results  on  various  types  of  boilers  and  with  various  fuels  have 
furnished  a  very  satisfactory  account  of  the  distribution  of  the  heat. 
The  "unaccounted-for"  quantity  has  ranged  from  2.1  per  cent  up  to 
7  per  cent  in  different  cases.  He  has  never  found  that  quantity  a 
minus  one. 

As  to  sampling  the  gases,  the  writer  has  found  satisfactory  results 
from  using  a  single  tube  unperf orated,  which  extends  into  the  flue  to 
a  central  point,  care  being  taken  to  so  locate  the  inlet  end  that  it  will 
receive  what  would  be  considered  a  fair  sample.  It  is  important  that 
the  connecting-tube  between  the  flue  and  the  instrument  should  be 
tight,  and  that  care  be  taken  to  thoroughly  exhaust  the  pipe  of  air 
before  the  sample  is  drawn.  The  connections  and  stop-cocks  about 
the  instrument  itself  should  be  tight  and  carefully  manipulated.  It 
is  of  the  first  importance  that  the  absorbing  liquids  be  in  good  condi- 
tion. It  is  well  for  the  engineer  himself  to  make  the  cuprous 
chloride  which  is  required  for  absorbing  the  carbonic  oxide,  and  to 
frequently  renew  it  in  the  apparatus. 

The  writer  has  found  it  desirable  to  locate  the  gas-apparatus  on 
the  boiler-room  floor,  near  by  the  furnaces  where  the  fires  are  being 
handled,  and  to  carry  the  gases  from  the  flue  to  the  Orsat  by  means 
of  a  lead  pipe  of  small  bore.  The  apparatus  can  then  be  manipulated 
in  plain  view  of  all  the  operations  going  on  in  the  fire-room,  and  in 
that  way  he  can  time  the  drawing  of  samples  to  good  advantage.  By 
using  proper  judgment  as  to  when  to  draw  the  sample,  satisfactory 
results  can  be  obtained  from  analyses  covering  momentary  drawings. 
For  the  purposes  of  the  boiler-test  and  working  of  the  heat-balance, 
it  is  preferred;  however,  that  the  drawings  should  cover  the  entire 
period  which  elapses  between  two  successive  firings. 

The  successful  manipulation  of  the  Orsat  apparatus  is  not  a  thing 
which  requires  expert  chemical  knowledge,  for  it  can  be  properly 
handled  by  any  one,  after  a  little  practice,  who  is  familiar  with  the 
operation  of  instruments  of  measurement. 

G.  H.  B. 

*  In  connection  with  this  subject  the  student  should  read  R.  S.  Bale's  paper  on 
"  Flue-gas  Analyses  in  Boiler  Tests,"  with  the  discussion  thereon,  Trans.  Am. 
Soc.  M.  E.,  vol.  xviii.  p.  901.  Consult  also  Gill's  "Fuel  and  Gas  Analyses," 
John  Wiley  &  Sons,  and  Hempel's  "  Gas  Analyses,"  Macmillan  &  Co. 

w.  K. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  367 

APPENDIX  XXXIV. 

SMOKE   MEASUREMENTS. 

In  a  series  of  competitive  trials  between  two  furnaces  which,  the 
writer  made  in  June,  1897,  for  the  Detroit  Water- works,  a  method  of 
obtaining  a  continuous  record  of  the  quantity  of  smoke  was  intro- 
duced, which  seems  to  him  of  great  value  in  making  specific  what  has 
heretofore  been  based  upon  the  judgment  of  the  person  conducting 
the  observations.  The  method  referred  to  consisted  simply  in  sus- 
pending, at  a  suitable  point  in  the  smoke-passage  between  the  boiler 
and  the  flue,  a  smooth,  flat,  brass  plate,  having  its  face  at  right  angles 
to  the  direction  of  the  current.  This  plate  served  to  collect  a  certain 
portion  of  the  soot  which  was  carried  along  by  the  waste  gases,  and 
indirectly  furnished  a  means  of  sampling  the  gas  in  respect  to  its 
smokiness.  The  plate  was  24  ins.  long  and  |  in.  wide,  and  it  pre- 
sented a  surface  amounting  to  21  sq.  ins.  Being  inserted  through  a 
hole  in  the  top  of  the  flue,  and  suspended  by  a  wire,  the  hole  being 
covered,  the  plate  could  be  readily  withdrawn  from  its  place  whenever 
desired,  and  the  collection  of  soot  removed  by  the  use  of  a  stiff  brush. 
This  was  done  every  two  hours  during  the  progress  of  the  trial.  The 
quantity  of  soot  which  collected  on  this  plate  varied  according  to  the 
type  of  the  furnace  and  the  character  of  the  fuel,  and  also  according 
to  the  conditions  of  the  firing  and  the  working  conditions  of  the 
boiler.  The  records  of  the  smoke-measuring  device,  and  those  of  the 
ocular  observations  of  the  chimney,  were  in  accord  with  each  other. 
The  quantity  of  soot  which  was  collected,  reduced  to  the  hourly  rate, 
varied  in  these  tests  from  9  to  184  milligrams.  The  method  has  not 
as  yet  been  tried  in  the  case  of  a  flue  carrying  very  dense  smoke. 

G.  H.  B. 

APPENDIX  XXXV. 

THE   RINGELMANN   SMOKE-CHART. 

Professor  Eingelmann,  of  Paris,  has  invented  a  system  of  deter- 
mining the  relative  density  or  blackness  of  smoke.  In  making 
observations  of  the  smoke  proceeding  from  a  chimney,  four  cards 
ruled  like  those  in  the  cut  (Fig.  116),  together  with  a  card  printed  in 
solid  black  and  another  left  entirely  white,  are  placed  in  a  horizontal 
row  and  hung  at  a  point  about  50  ft.  from  the  observer  and  as  nearly 
as  convenient  in  line  with  the  chimney.  At  this  distance  the  lines 
become  invisible,  and  the  cards  appear  to  be  of  different  shades  of 
gray,  ranging  from  very  light  gray  to  almost  black.  The  observer 
glances  from  the  smoke  coming  from  the  chimney  to  the  cards,  which 
are  numbered  from  0  to  5,  determines  which  card  most  nearly  corre- 
sponds with  the  color  of  the  smoke  and  makes  a  record  accordingly, 
noting  the  time.  Observations  should  be  made  continuously  during 


368 


STEAM-BOILER  ECONOMY. 


No.  1. 


No.  2. 


No.  3.  No.  4. 

FIG.  116. — THE  RINGELMANN  SCALE  FOR  GRADING  THE  DENSITY  OF  SMOKE.. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  369 

ssay  one  minute,  and  the  estimated  average  density  during  that  minute 
recorded,  and  so  on,  records  being  made  once  every  minute.  The 
.average  of  all  the  records  made  during  a  boiler-test  is  taken  as  the 
average  figure  for  the  smoke  density  during  the  test,  and  the  whole  of 
the  record  is  plotted  on  cross-section  paper  in  order  to  show  how  the 
smoke  varied  in  density  from  time  to  time.  A  rule  by  which  the 
cards  may  be  reproduced  is  given  by  Professor  Bingelmann  as  follows : 

Card  0— All  white.     . 

Card  1 — Black  lines  1  mm.  thick,  10  mm.  apart,  leaving  spaces 
9  mm.  square. 

Card  2 — Lines  2.3  mm.  thick,  spaces  7.7  mm.  square. 

Card  3 — Lines  3.7  mm.  thick,  spaces  6.3  mm.  square. 

Card  4 — Lines  5.5  mm.  thick,  spaces  4.5  mm.  square. 

Card  5— All  black. 

The  cards  as  printed  on  the  opposite  page  are  much  smaller  than 
those  used  by  Professor  Eingelmann,  but  the  thickness  and  the 
spacing  of  the  lines  are  the  same. 

w.  K. 

APPENDIX  XXXVI. 

STARTING   AND    STOPPING    A   TEST. 

Of  the  two  methods  of  starting  and  stopping  a  test,  the  so-called 
'"  standard  "  method  and  the  "  alternate  "  method,  the  writer  prefers 
the  latter,  believing  that  the  errors  in  the  estimation  of  the  quantity 
and  condition  of  the  small  amount  of  coal  left  on  the  grate  after 
cleaning  are  less  than  the  errors  of  the  "  standard  "  method,  which 
are  due:  first,  to  cooling  of  the  boiler  at  the  beginning  and  end  of  the 
test ;  second,  to  the  imperfect  combustion  of  the  fuel  at  the  beginning ; 
and  third,  to  excessive  air-supply  through  the  thin  fire  while  burning 
down  before  the  end  of  the  test. 

A  special  caution  is  needed  against  a  modification  of  the  "  alter- 
nate" method,  which  has  been  adopted  by  some  testing  engineers 
within  the  past  few  years.  It  consists  in  taking  the  starting  and  the 
stopping  times  each  at  a  time  subsequent  to  the  cleaning,  say  after 
400  Ibs.  of  coal  has  been  fired  since  the  cleaning.  There  are  two 
sources  of  serious  error  in  this  method,  one  causing  an  incorrect 
measurement  of  the  coal,  the  other  an  incorrect  measurement  of  the 
water.  Suppose  200  Ibs.  of  hot  coke  are  left  on  the  grate  at  the  end 
of  cleaning  and  400  Ibs.  of  fresh  coal  are  added  by  the  end  of,  say, 
half  an  hour  after  cleaning.  If  the  coal  left  at  the  end  of  the  clean- 
ing, and  the  boiler-walls  also,  are  very  hot,  and  the  coal  is  highly 
volatile  and  dry  and  the  pieces  of  such  size  as  not  to  choke  the  air- 
supply,  the  fire  may  burn  so  briskly  that  at  the  end  of  the  half -hour 
the  fuel-value  of  the  partly-burned  coal  left  out  of  the  total  600  Ibs. 
is  equivalent  only  to  200  Ibs.  of  coal.  If,  on  the  contrary,  the  hot 
coke  on  the  grates  at  the  end  of  the  cleaning,  and  the  boiler-walls, 
.are  considerably  cooled,  if  the  fresh  coal  fired  is  moist  and  of  small 


3 TO  STEAM-BOILER  ECOONMT. 

size,  such  as  the  slack  of  run-of-mine  bituminous  coal,  which  is  often 
found  in  one  portion  of  a  pile  in  greater  quantity  than  in  another,  the 
fire  during  the  half -hour  may  burn  so  sluggishly  that  the  coal  and 
coke  on  the  grate  at  the  end  of  the  half-hour  may  have  a  fuel-value 
equal  to  400  Ibs.  of  coal.  If,'  in  this  case,  it  is  assumed  that  the 
quantity  and  condition  of  the  coal  at  the  end  of  the  half -hour  after 
cleaning  are  the  same  at  the  starting  and  stopping  time ;  and,  if  the 
fire  burned  briskly  during  the  half -hour  before  starting  and  slowly 
during  the  half-hour  before  stopping,  the  boiler  will  be  charged  with 
more  coal  than  was  actually  burned.  If,  on  the  contrary,  the  coal 
burns  away  more  slowly  during  the  half -hour  after  the  cleaning  before 
the  starting  time  and  more  rapidly  during  the  half -hour  before  the 
end  of  the  test,  the  boiler  is  not  charged  with  as  much  coal  as  was 
actually  burned. 

The  error  in  water-measurement  is  due  to  the  fact  that  the  con- 
dition of  the  fire,  and  especially  the  quantity  of  flaming  gases  arising 
from  it,  influences  the  height  of  the  water-level.  A  bright  hot  fire,  or 
a  fire  with  an  abundance  of  burning  gas  proceeding  from  it,  causes 
the  water-level  to  rise;  while  anything  that  cools  the  furnace,  such 
as  freshly-fired  coal,  an  open  fire-door,  or  a  check  to  the  draft, 
causes  the  water-level  to  fall.  A  rise  or  a  fall  of  several  inches  in  a 
few  seconds  frequently  occurs  when  bituminous  coal  is  used.  If  the 
water-level  is  noted  at  the  starting  of  the  test,  when  it  is  raised  by  a 
bright  fire,  and  at  the  end  of  a  test,  when  it  is  depressed  by  the 
stoppage  of  violent  ebullition  or  of  rapid  circulation,  due  to  the  cool- 
ing of  the  fire,  the  boiler  will  be  credited  with  more  water  than  was 
really  evaporated,  and  vice  versa. 

The  only  correct  times  to  be  noted  as  the  starting  and  the  stopping 
times  are  when  the  smallest  amount  of  fuel  is  on  the  grate  and  when 
it  is  in  the  most  burned-out  condition ;  that  is,  just  before  firing  fresh 
coal  after  cleaning,  and  when  the  water-level  is  in  its  most  quiet  con- 
dition and  the  least  raised  by  ebullition.  The  furnace-door  has  then 
been  kept  open  for  some  time  for  cleaning  and  the  furnace  there- 
fore is  in  its  coolest  state.  This  condition  of  fire  and  of  water-level 
can  be  duplicated  immediately  after  cleaning  the  fire;  but  there  is  no 
certainty  of  duplication  of  any  condition  when  there  is  a  bright  fire 
and  consequent  rapid  steaming. 

These  statements  are  not  based  upon  theoretical  considerations, 
but  are  the  results  of  many  experiments  made  by  the  writer  to  deter- 
mine the  best  starting  and  stopping  times.  In  a  long  series  of  tests 
with  bituminous  coals  no  less  than  six  different  times  were  recorded 
as  starting  times  and  as  many  as-  stopping  times,  and  the  coal 
apparently  used  and  the  water  apparently  evaporated  recorded  and 
calculated  for  each.  These  times  were:  A,  before  opening  the  first 
or  right-hand  door  to  clean  the  fire ;  B,  after  cleaning  the  first  half 
of  the  furnace  and  just  before  firing  fresh  coal ;  (7,  after  cleaning  the 
second  half  of  the  furnace ;  /),  after  200  Ibs.  of  fresh  coal  had  been 
fired;  E,  after  400  Ibs.;  F,  after  600  Ibs.  By  plotting  the  apparent 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  371 

water-evaporation  between  A  and  E,  both  for  starting  and  for 
stopping  times,  it  was  seen  that  there  was  nearly  always  an  apparent 
negative  evaporation  between  B  and  D,  and  sometimes  between  B  and 
C  and  between  B  and  E,  due  to  the  correction  for  height  of  observed 
water-level,  the  level  rising  rapidly,  being  much  greater  than  the 
water  fed  by  the  pump.  There  was  often  no  similarity  of  appearance 
of  the  plotted  diagrams  between  A  and  F  at  the  beginning  and  at  the 
end  of  the  same  test.  The  possible  error  of  water-measurement  due 
to  taking  A,  D,  E,  or  /Tas  the  starting  time  Avas  sometimes  as  much 
as  2000  Ibs.  of  water,  or  about  3  per  cent  of  the  whole  amount 
evaporated  in  a  ten-hour  test.  The  record  of  water  evaporated 
between  the  stopping  and  starting  times  C  occasionally  differed  con- 
siderably from  that  taken  between  the  B  start  and  stop,  due  to  the 
fact  that  sometimes  between  B  and  C  there  was  a  sudden  lighting  up 
of  the  fresh  coal  on  the  cleaned  side  of  the  furnace,  while  at  other 
times  the  fire  would  not  light  up  brightly  until  after  the  C  point  had 
passed.  It  was  therefore  decided  that  the  B  time,  when  the  furnace 
was  the  coldest  and  the  water-level  at  the  lowest,  was  the  only  time 
which  could  be  accepted  as  the  true  starting  and  stopping  time. 

AV.  K. 

APPENDIX  XXXVII. 

STAKTING    AND    STOPPING    A   TEST. 

Between  the  "standard"  method  and  the  "alternate"  method  of 
starting  and  stopping  a  test  I  believe  the  standard  method,  if  properly 
followed,  is  the  more  reliable  of  the  two  for  determining  absolutely 
correct  and  unquestionable  results.  One  of  the  important  matters 
which  the  standard  method  determines  accurately  is  the  absolute 
quantity  of  ash  and  refuse.  In  the  case  of  the  alternate  method  it  is 
extremely  difficult  to  obtain  the  quantity  of  ash  in  such  a  way  as  to 
be  positively  reliable,  for  the  reason  that  in  cleaning  the  fire  it  is 
hardly  possible  to  leave  the  same  amount  of  ash,  clinkers,  and  refuse 
mixed  with  the  coal  at  one  time  as  at  the  other.  When  the  fire  is 
started  new  with  wood,  and  burned  out  at  the  end  of  the  trial,  as  it  is 
in  pursuing  the  standard  method  of  starting  and  stopping,  there  is 
absolutely  no  chance  of  making  an  error  of  this  nature.  The  ten- 
dency of  nearly  all  parties  concerned  in  a  boiler-test  is  to  have  the 
boiler  make  a  good  showing,  and  it  is  the  rule  rather  than  the  excep- 
;  tion  that  the  fire  at  the  end  of  the  test  is  burned  lower,  if  anything, 
than  it  was  at  the  beginning,  so  as  to  surely  give  the  boiler  all  the 
advantage  to  which  it  is  entitled.  With  this  tendency  the  cleaning 
of  the  fire  at  the  end  of  the  test  is  apt  to  be  less  thorough  than  at  the 
beginning,  so  that  in  the  first  place  no  fuel  will  be  lost,  and  in  the 
second  place  that  the  bed  of  coal  may  not  be  reduced  in  thickness  any 
lower  than  is  absolutely  necessary.  The  result  is  that  the  bed  of  coal 
at  the  end  is  apt  to  contain  more  waste  material,  which  belongs  with 
the  ashes,  than  it  does  at  the  beginning,  and  this  is  one  of  the  reasons 


372 


STEAM-BOILER  ECONOMY. 


why  the  alternate  method  of  starting  and  stopping  a  test  is  objec- 
tionable. 

There  appears  to  be  confusion  in  the  minds  of  some  experts  as  to 
the  facility  with  which  a  new  fire  can  be  started  with  wood.  They 
appear  to  hold  the  belief  that  there  is  apt  to  be  a  great  loss  in  getting 
a  new  fire  started  in  this  way,  a  loss  which  occurs  not  only  in  the 
matter  of  time,  but  also  in  the  matter  of  combustion  and  heat.  I 
have  made  a  great  many  tests,  using  the  standard  method  of  starting 
and  stopping,  and  my  experience  has  been  that,  so  far  as  facility  of 
manipulation  is  concerned,  it  is  perfectly  easy  and  satisfactory  to  use 
the  standard  method.  With  a  suitable  quantity  of  dry  piiie-wood, 
preferably  in  the  form  of  edgings,  or  1-in.  boards  which  have  been 


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FIG.  117. — GRAPHIC  RECORD  OF  A  BOILER-TEST. 

split  into  narrow  pieces,  it  is  quite  feasible  to  draw  the  old  fire,  kindle 
a  new  one,  and  have  the  boiler  under  steam  in  practically  a  normal 
condition  of  running,  with  the  coal  selected  (supposing  this  to  be  a 
good  quality  of  bituminous  or  semi-bituminous  coal)  inside  of  15 
minutes'  time.  My  opinion  is  that  the  objections  which  have  been 
raised  to  starting  with  wood  fires  is  due  to  the  fact  that  suitable  pre- 
paration has  not  been  made  in  the  matter  of  furnishing  a  proper  kind 
of  wood  cut  into  proper  shape.  Certainly  it  is  impossible  to  start  a 
satisfactory  new  fire  if  the  supply  of  wood  contains  any  appreciable 
quantity  of  wet  material  or  hard  wood,  or  wood  which  is  in  thick 
pieces  which  do  not  readily  ignite.  I  have  myself  had  difficulty  in 
starting  a  test  under  these  circumstances,  and  I  have  no  doubt  that 
experts  who  have  found  the  standard  method  objectionable  have 
encountered  the  same  obstacle  and  they  probably  base  their  objections 
largely  at  least  on  these  unnecessary  difficulties.  G.  11.  B. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  373 

APPENDIX  XXXVIII. 

CHART   SHOWING    GRAPHICALLY   THE   LOG    OF   A   TRIAL. 

The  well-known  method  of  plotting  observations  and  data  on 
cross-section  paper,  and  making  a  chart  applying  to  the  test,  is  a 
useful  means  of  representing  the  exact  uniformity  of  conditions  exist- 
ing during  a  trial.  Such  a  chart  is  illustrated  in  the  appended  cut 
(Fig.  117),  in  which  the  abscissse  represent  times  and  the  ordinates  on 
appropriate  scales  the  various  observations  and  data. 

G.  H.  B. 

APPENDIX  XXXIX. 

CONTINUOUS    DETERMINATIONS    OF   CARBONIC    ACID   IN    FLUE-GASES. 

Various  forms  of  apparatus  have  been  devised  for  showing  con- 
tinuously the  percentage  of  carbonic  acid  in  waste  gases,  and  instru- 
ments of  this  kind,  if  reliable,  serve  a  useful  purpose  in  the  management 
of  the  fires  during  the  progress  of  a  test.  Among  these  instruments 
may  be  mentioned  the  "gas-balance"  of  Alphonse  Custodis,  the 
Arndt  "  econometer,"  and  the  Uehling  &  Steinbart  "  gas  composi- 
meter." 

G.  H.  B. 

APPENDIX  XL. 

MEASURING    RADIATION    FROM    CERTAIN    TYPES    OF    BOILERS. 
(Contributed  by  Mr.  R.  S.  Hale,  Member  of  the  Society.) 

While  the  heat  lost  by  radiation  is  only  a  small  amount  of  the 
total  heat  if  the  boiler  is  well  covered,  yet  it  is  important  enough  to 
be  considered,  and  in  the  case  of  certain  internally-fired  boilers,  such 
as  the  ordinary  upright  vertical,  the  Manning,  the  marine,  the 
Thornycroft,  etc.,  it  can  be  easily  determined  by  at  least  two 
methods.  If  the  boiler  is  covered  completely  (or  nearly  so)  with  any 
boiler-covering  for  which  the  rates  of  flow  of  heat  can  be  or  have  been 
determined,  then  the  total  loss  of  heat  is  easily  computed.  Thus, 
Norton's  tests  (Trans.  Am.  Soc.  M.  E.,  vol.  xix.  p.  729)  give  the  flow 
per  square  foot  per  hour  at  various  differences  of  temperature  for 
many  frequently-used  coverings.  Now  if  the  temperature  of  the 
steam  and  of  the  air  and  the  total  exposed  area  is  known,  the  loss 
from  the  whole  boiler  per  hour  is  easily  computed,  and  this  loss 
divided  by  the  total  heat  supplied  in  the  same  time  gives  the  percen- 
tage loss  by  radiation.  If  the  boiler  is  only  partially  covered,  the  loss 
from  the  covering  and  from  the  bare  iron  can  be  computed  separately. 

The  second  method  of  determining  the  radiation  loss  is,  after 
drawing  the  fire,  to  shut  all  doors  and  dampers  tight,  and  then  to 


UNIVERSITY  ] 

OF  J 

\^' 


374 


STEAM-BOILER  ECONOMY. 


note  the  time  necessary  for  the  steam-pressure  to  fall  say  10  or  20  Ibs. 
The  fall  in  pressure  gives  the  data  from  which  the  fall  in  temperature 
can  be  computed  by  means  of  the  steam-tables,  and  the  total  loss  of 
heat  in  thermal  units  is  equal  to  the  weight  of  iron  and  water  multi- 
plied by  their  respective  specific  heats  and  the  fall  of  temperature. 
This  divided  by  the  time  gives  the  total  heat-units  lost  by  radiation 
per  hour,  and  the  percentage  loss  by  radiation  is  found  as  before  by 
dividing  by  the  total  heat  supplied. 

It  should  be  noted  that  the  first  method  given  does  not  apply 
unless  the  boilers  are  internally-fired.  Neither  does  the  second 
method  apply  if  there  is  any  brick  in  the  furnace,  or  setting,  since  the 
method  depends  on  the  assumption  that  the  temperature  of  the  water 
and  iron  corresponds  to  the  steam-pressure,  which  would  not  be  true 
of  the  brick.  The  second  method  is  also  apt  to  give  high  results,  as 
it  is  almost  impossible  to  absolutely  close  the  doors  and  dampers,  and 
air  leaking  past  them  carries  heat  up  the  chimney,  in  addition  to  the 
true  radiation. 

APPENDIX  XLI. 

DETERMINATION    OF    THE    MOISTURE    IN    STEAM  FLOWING    THROUGH    A 

HORIZONTAL    PIPE. 

(Contributed  by  D.  S.  Jacobus,  Member  of  the  Society.} 
In  some  cases  it  is  impossible  to  place  the  sampling  nozzle  in  a 
vertical  steam-pipe  rising  from  the  boiler  as  recommended  in  Article 
XIV  of  the  Code.  When  this  is  the  case  and  it  is  possible  to  connect 
to  a  horizontal  steam-pipe,  the  arrangement  of  throttling  calorimeters 
shown  in  Fig.  118  gives  satisfactory  results. 


FIG.  118. — ARRANGEMENT  OF  THREE  STEAM  CALORIMETERS  IN  A  HORIZONTAL 

PIPE. 

The  calorimeter  A  is  attached  to  the  separator  G,  which  is  in  turn 
attached  to  the  under  side  of  the  steam-pipe  by  the  nipple  D.  The 
nipple  D  is  made  flush  with  the  bottom  of  the  pipe.  The  calorimeter 
B  is  attached  to  a  nozzle  having  no  side-holes,  which  passes  through 
the  stuffing-box  E.  This  nozzle  is  adjustable  so  that  the  steam  can 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  375 

be  drawn  from  any  height  in  the  pipe.  When  in  its  lowest  position 
it  is  flush  with  the  bottom  of  the  pipe.  The  calorimeter  C  is  attached 
to  the  perforated  nipple  F.  The  calorimeters  are  placed  at  some  dis- 
tance from  an  elbow  or  bend,  so  that  if  there  is  moisture  in  the  steam 
it  tends  to  run  along  the  bottom  of  the  pipe.  This  moisture  will  flow 
into  the  nipple  D  and  collect  in  the  separator  G.  Nearly  all  the 
moisture  may  sometimes  be  drawn  out  in  this  way,  and  if  the  calo- 
rimeters B  and  C  indicate  dry  steam,  the  weight  of  moisture  collected 
in  G  represents  the  entire  moisture  in  the  steam.  The  three  calorim- 
eters are  all  covered  in  the  same  way  to  diminish  radiation,  and  the 
normal  reading  of  the  thermometers  /and  J  used  in  the  calorimeters 
B  and  C  can  ordinarily  be  obtained  by  placing  them  in  the  calorim- 
eter A.  The  perforated  nipple  F  serves  to  show  that  there  is  no 
moisture  distributed  through  the  steam,  and  in  the  case  of  a  sudden 
belch  of  moisture  it  will  indicate  the  same.  Barrus  calorimeters  were 
used  in  our  tests,  and  the  calorimeter  A,  combined  with  the  separator 
G,  forms  in  reality  a  Barrus  Universal  Calorimeter.  With  a  properly- 
constructed  separator,  the  steam  passing  through  the  calorimeter  A 
will  be  practically  dry  with  as  high  as  60  Ibs.  of  moisture  drawn  from 
the  separator  per  hour,  and,  until  this  limit  is  exceeded,  the  normal 
readings  of  the  thermometers  used  in  the  calorimeters  B  and  C  may 
be  obtained  by  placing  them  in  the  calorimeter  A,  as  has  already  been 
.stated. 

In  some  cases  the  calorimeter  C  is  omitted  and  the  amount  of 
moisture  is  determined  by  means  of  the  separator,  with  the  adjustable 
nozzle  at  E  and  the  separator  and  calorimeter  A. 

The  percentage  of  priming  P  for  the  steam  passing  through  the 
calorimeters  B  and  C  is  given  by  the  formula, 


where  P  =  the  percentage  of  priming; 

N  =  the  normal  reading,  in  degrees  Fahrenheit,  obtained  by 

placing  the  thermometers  in  A', 
T  =  the  reading  when  placed  in  either  B  or  C', 
L  =  the  latent  heat  at  the  pressure  of  the  steam  in  the  steam- 

main  in  British  thermal  units  per  pound. 

It  is  best  to  employ  the  normal  reading,  as  Mr.  Barrus  recom- 
mends, in  calculating  the  moisture  corresponding  to  the  readings  of 
a  throttling  calorimeter,  and  not  the  formula  given  in  Appendix  XY 
of  the  Code  ;  for  if  the  formula  given  in  Appendix  XV  is  used,  the 
mercury-thermometer  used  to  measure  the  temperature  of  the  steam, 
after  passing  through  the  orifice,  must  be  corrected  for  the  error  pro- 
duced in  not  heating  the  entire  length  of  the  stem,  and  must  also 
be  corrected  to  make  the  readings  correspond  with  those  that  would 
be  given  by  an  air-thermometer.  The  radiation  of  the  calorimeter 
must  also  be  determined  by  a  separate  experiment,  and  allowed  for. 
When  the  normal  reading  is  taken,  as  Mr.  Barrus  recommends,  all 
errors  of  radiation  and  corrections  for  the  thermometers  are  eliminated. 


376  STEAM-BOILER  ECONOMY. 

The  normal  reading  should  be  obtained  either  by  connecting  the> 
calorimeter  to  a  vertical  nipple,  with  no  side-holes,  which  projects 
upward  in  a  horizontal  steam-pipe,  in  which  the  steam  is  in  a 
quiescent  state,  or  it  should  be  obtained  by  connecting  the  calorimeter 
to  a  separator,  which  is  known  to  remove  all  the  moisture.  The 
normal  reading  should  not  be  determined  when  the  calorimeter  is 
attached  to  a  horizontal  nipple  with  side-holes,  placed  in  a  vertical 
pipe,  because  should  this  be  done  the  readings  may  be  low  on  account 
of  moisture,  which  may  fall  through  the  steam  and  cling  to  the  noz- 
zle, and,  finally,  be  drawn  into  the  calorimeter. 

The  results  given  by  a  throttling  calorimeter  cannot  be  relied  on 
within  one-fifth  of  1  per  cent,  because  experiments  have  shown  that 
the  quality  of  the  "  dead  steam  "  used  in  obtaining  the  normal  read- 
ings may  vary  by  this  amount.*  As  tne  quality  of  the  "  dead  steam  "" 
may  not  be  that  of  the  steam  used  by  Regnault  in  his  experiments,, 
there  may  be  a  still  greater  error.  When  the  formula  given  in 
Appendix  XV  of  the  Code  is  used,  the  probable  error  is  not  eliminated,, 
for  a  study  of  Regnault's  Experiments  shows  that  the  value  used  in 
the  formula  for  the  specific  heat  of  superheated  steam  may  be  slightly 
in  error  for  the  conditions  involved  in  a  throttling  calorimeter.. 
Experiments  have  shown  that  the  two  methods  of  computing  the^ 
moisture  agree  within  one-fifth  of  1  per  cent  when  the  proper  correc- 
tions are  made  for  radiation  and  when  the  temperatures  are  reduced 
to  the  equivalents  by  an  air-thermometer. f  These  experiments  were 
made  at  the  single  pressure  of  80  Ibs.  per  sq.  in.  above  the  atmos- 
phere, and  it  has  not  been  shown  that  the  two  methods  agree  within 
this  amount  at  all  pressures,  but  as  there  should  be  no  discrepancy 
provided  the  specific  heat-factor  remains  constant  for  the  conditions 
involved,  it  is  probable  that  the  two  methods  agree  very  nearly  with 
each  other  at  all  pressures.  J 

Computation  of  the  Eesults  of  a  Boiler-trial. — The  following  ex- 
ample shows  a  convenient  method  of  making  the  calculations  of  the 
results  of  a  trial  from  the  observed  data  recorded  at  the  trial. 

The  observed  data  used  in  the  calculations  are  : 

a.  Duration  of  the  test 10  hrs.  15  min.  =  10.25  hrs. 

b.  Water  apparently  evaporated .Ibs.  30,000 

c.  Coal  used Ibs.  8,000 

d.  Feed-water  temperature,  average 110°  F. 

e.  Steam-pressure  by  gauge,  average Ibs.  120 

/.  Moisture  in  tbe  coal $2 

g.  Moisture  in  tbe  steam $  0.5 

h.  Asb  and  refuse  withdrawn  from  the  fire 6$  =  Ibs.  ISO' 

i.    Grate-surface sq.  f t.  30 

j.    Heating  surface sq.  ft.  1,000- 

*  Trans.  Am.  Soc.  M.  E.,  vol.  xvi.  p.  466. 

f  Trans.  Am.  Soc.  M.  E.,  vol.  xvi.  p.  460. 

jit  must  not  be  inferred  from  this  that  tbe  author  considers  the  specific  heat 
of  steam  to  be  the  same  at  all  pressures.  On  the  contrary,  he  has  made  experi- 
ments which  show  that  this  is  not  the  case. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  37T 

The  following  results  are  calculated  from  these  data  : 
yfc.  Factor  of  evaporation,  from  d  and  e,  taken  from  table  of  factors,  1.15. 
bi  Water  evaporated,  corrected  for  moisture  in  the  steam  =  6  —  gb  =  30,000  —  150> 

=  29,850  Ibs. 
U.E.  Water  evaporated  from  and  at  212°  into  dry  steam  =  blX^=  29,850  X  1.15. 

=  34, 327  Ibs. 

d  Dry  coal  =  c-f=  3000  -  60  =  2940  Ibs. 
ca  Combustible  =  Ci  —  7*  =  2940  —  180  =  2760  Ibs. 

USEFUL   RESULTS. 

(1)  j_5-c  Water  apparently  evaporated  per  Ib.  coal,  actual  conditions  30,000  -j- 

3000  =  10  Ibs. 

(2)  U.E.  -f-c  Water  evaporated  from  and  at  212°  per  Ib.  coal,  34,327  -f-  3000  =• 

11. 442  Ibs. 

(3)  U.E.  -T-CI   Water  evaporated  from  and  at  212°  per  Ib.  dry  coal,  34327-^2940 

=  11.676. 

(4)  U.E.  -5-ca  Water  evaporated  from  and  at  212°  per  Ib.  combustible,  34,327  -f- 

2760  =  12.437  Ibs. 

(5)  H.P.  Horse- power  =  U.E.  -j-a-s-  34. 5  -34, 327  n-1 0.25-^-34.5  =  97.1  H.  P. 

(6)  Coal   per    sq.    ft.    grate-surface   per   Lour,    c-e-  a-t-  i  =  3000  -H  10.25  -T-  30  = 

9.76  Ibs. 

(7)  U.E.    per  sq.  ft.  heating  surface  per  hour,  U.E.  -5-  a  ~-j  —  34,327  -f- 10.25 -=-~ 

1000  =  3.35  Ibs. 

(8)  T.  Temperature  of  the  chimney  gases,  average  450°  F. 

Interpretation  of  the  above  results. — The  results  given  in  the  last 
eight  lines  are  the  ones  that  give  practically  all  the  information  that 
is  required  from  any  boiler-trial.  All  the  observed  data  and  all  the 
computations  are  of  use  only  for  the  purpose  of  obtaining  these  eight 
results.  We  will  now  consider  what  conclusions  may  be  drawn  by  an 
engineer  from  these  eight  results  alone,  the  figures  themselves  being 
accepted  as  correct. 

1.  From  the  result,  10  Ibs.  of  water  evaporated  under  actual  con- 
ditions, nothing  can  be  known  concerning  the  efficiency  of  the  boiler 
or  the  quality  of  the  coal,  unless  the  conditions  of  feed-water  tem- 
perature, steam-pressure,  and  moisture  in  the  coal  and  in  the  steam 
are  also  known.  About  the  only  use  that  can  be  made  of  this  figure 
is  in  connection  with  estimates  of  the  cost  of  steam-power.  If  the 
engine  using  the  steam  furnished  by  the  boiler  uses  20  Ibs.  of  steam 
per  horse-power  per  hour,  then  it  will  require  20  -j-  10  =  2  Ibs.  of 
coal  per  horse-power,  the  "  actual  conditions  "  under  which  the  boiler 
is  operated  being  the  pressure  of  steam  required  by  the  engine  and  the 
temperature  of  water  in  the  hot-well  of  the  condenser  or  in  the  feed- 
water  heater,  both  of  which  obtain  their  heat  from  the  exhaust  steam 
furnished  by  the  engine. 


3T8  STEAM-BOILER  ECONOMY. 

2.  The  result,   11.442  Ibs.  evaporated  from  and  at  212°  per  Ib.  of 
coal,  is  useful  as  a  measure  of  the  quality  of  the  coal,  provided  the  effi- 
ciency of  the  boiler  is  known.     For  tests  of  different  coals  with  the 
same  boiler  and  under  the  same  conditions  of  rate  of  driving,  kind  of 
firing,  etc.,  this  figure  is  the  one  that  will  be  used  in  comparing  the 
relative  values  of  the  coals.     It  is  a  very  high  figure,  and  indicates 
both  that  the  coal  is  of  good  quality  and  that  the  efficiency  of  the 
boiler  is  high. 

3.  The  result,  11.676  U.E.  per  Ib.  of  dry  coal,  is  useful  in  connec- 
tion with  result  2,  as  a  measure  of  the  quality  of  the  coal.     The  dif- 
ference between  the  two  results  being  2$  shows  that  that  is  the  per- 
centage of  moisture  in  the  coal,  and  this  would  indicate  that  the  coal 
is  not  Western   coal.     The  result  would  also  be  used  in  comparing 
tests  of  coals  of  one  grade,  but  differing  in  surface-moisture,  so  as  to. 
reduce  them  all  to  the  standard  of  dry  coal.     It  is  practically  of  no 
use    in   comparing  coals  of  different  grades,   such  as  Pittsburg  and 
Illinois  coals,  containing,  respectively,  say  2$  and  12$  of  moisture. 

4.  The  result,  12.437  U.E.  per  Ib.  of  combustible,  is  the  one  used 
for  comparing  boiler  efficiencies.      If  the  grade  of  coal  is  known,  and 
its  heating  value  per  Ib.  of  combustible  is  either  known  as  the  result 
of  a  calorimetric  test  or  by  computation  from  analysis,  or  estimated 
from  the  average   heating  value  per  Ib.  combustible  of  coal  of  that 
grade,  then  the  figure  12.437  divided  by  the  quotient  of  the  heating 
value  of  the  coal  divided  by  965.7  will  give  the  efficiency.      The 
figure  12.437  being  in  excess  of  12  Ibs.,  which  is  practically  the  max- 
imum value  obtainable  for  anthracite,  and  beyond  the  maximum  for 
bituminous  coal,  indicates  both  that  the  coal  is  semi-bituminous  and 
that  the  boiler  was  operated  with  a  very  high  efficiency.       Taking  the 
average  heating  value  of  semi-bituminous  coal  at  15,750  B.T.U.  per 

12  437 

Ib.  combustible,  gives  -  ——-  =  76.26$  efficiency. 

15,750  -f-  96o.7 

5.  The  result,  97.1  H.P.,  is  the  measure  of  the  capacity  of  the 
boiler  developed  in  the  trial.       This  figure  will  be  compared  with  the 
boiler's  rated  or  nominal  capacity. 

6.  The  result,  9.76  Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour,  is  the 
measure  of  rate  of  driving  of  the  grate-surface.     It  is  a  rather  low 
figure  for  semi-bituminous  coal  in  average  practice.      Taken  in  con- 
nection with  the  high  efficiency  it  indicates  exceptionally  good  firing, 
very  nico  adjustment  of  the  thickness  of  bed  of  coal  on  the  grate  to 
the  force  of  the  draft,  and  an  excellent  furnace,  a  combination  of  fav- 
orable conditions  not  often  obtained. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  379 

7.  The  rate  of  driving,  3.35  U.E.  per  sq.  ft.  of  heating  surface  per 
Lour,  is  a  little  higher  than  that  at  which  maximum  economy  is  to  be 
expected,  but,  with  the  exceptionally  favorable  conditions  mentioned 
in  the  preceding  paragraph,  it  may  be  the  rate  corresponding  to  max- 
imum economy  in  this  case. 

8.  The  temperature  of  the  chimney-gases,  450°  F.,  is  unusually  low 
for  semi-bituminous  coal  in  ordinary   practice.     It  indicates,  when 
taken  in  connection  with  the  high  efficiency,  which  is  inconsistent 
with  air-leaks  in  the  setting,  a  high  furnace  temperature  and  a  clean 
boiler,  both  of  which  tend  to  produce  a  low  chimney  temperature. 


CHAPTER   XV. 


RESULTS  OF  STEAM-BOILER  TRIALS. 

IK  this  chapter  the  results  of  trials  of  several  different  boilers  will 
be  given,  together  with  comments  which  may  be  useful  to  students 
of  the  subject.  Mere  tables  of  results  of  individual  boiler-tests  are 
of  little  use  until  they  are  collated  and  compared  with  a  view  to  dis- 
cover the  various  causes  or  conditions  which  contributed  to  the  results 
obtained. 

Eange  of  Economy  found  in  Actual  Practice.— In  Donkin's  "  Heat 
Efficiency  of  Steam-boilers  "  there  are  fifty  tables  containing  the  results 
of  425  experiments  on  boilers  of  different  types.  The  following  table 
is  a  brief  summary  of  the  highest,  lowest,  and  mean  efficiencies  obtained 
in  405  experiments  with  different  boilers  without  economizers. 

EFFICIENCY    PER    CENT. 


Z 

!j 

if 

sl 

°  s 

4 

11 

2 

«„  S3 

sl 

£$ 

2a 

G  0) 

°s 

3 

1! 

tw  3 

Type  of  Boiler. 

815 

o  03 

%  ® 

51 

Type  of  Boiler. 

»'E 

js  D 

otf 

"S  ® 

cr 

!& 

l« 

*  ® 
m 

|| 

oW 

s  ft 

1- 

is, 

5  x 
S« 

§* 

8  9) 

11 

2* 

it' 

a« 

Water-tube*  . 

6 

84.1 

66.6 

77.4 

Elephant  

7 

70.8 

58.9 

65.3 

Locomotive.  . 

37 

83.3 

53.7 

72.5 

Water-tube  f.  . 

49 

77.5 

50.0 

64.9 

Lancashire.  .  . 

10 

74.4 

65.6 

72.0 

Lancashire..  .  . 

40 

73.0 

51.9 

64.2 

Two-story 

q 

76.1 

57.6 

70.3 

8 

65  9 

60  0 

62  7 

Two-story  .... 

29 

79.8 

55.9 

69.2 

Lancashire.  ... 

107 

79.5 

42.1 

62.4 

Dry-back       . 

94 

75.7 

64.7 

69.2 

Dry-  back  

6 

73.4 

54  8 

61  0 

Return  smoke- 

Lancashire  ^  .  . 

6 

06.7 

52.0 

59.4 

tube  

11 

81.2 

56.6 

68.7 

Elephant  

8 

65.5 

54.9 

58  5 

?,5 

81.7 

53.0 

68.0 

Lancashire..  .  . 

8 

74.3 

45.9 

57.3 

Cornish        .  .  . 

9 

81.0 

55.0 

67.0 

5 

76.5 

44  2 

56  2 

Wet-back..,.. 

6 

69.6 

62.0 

66.0 

*  IJ^-in.  tubes.        t4-in.  tubes.        $  Three-flue. 

About  the  only  conclusions  that  may  be  drawn  from  this  table  are- 
that  with  many  different  varieties  of  boiler  there  may  be  obtained  effi- 
ciencies which  are  so  high  as  to  be  scarcely  credible;  that  with  the  same 

380 


RESULTS  OF  STEAM-BOILER   TRIALS.  381 

types  of  boilers  in  other  trials  the  results  are  so  low  that  they  can  only 
be  accounted  for  by  improper  firing  or  some  other  unfavorable  condi- 
tion; and  that  economy  does  not  depend  on  the  type  of  boiler.  In  107 
tests  of  Lancashire  two-flue  boilers  the  efficiencies  varied  from  79.5 
down  to  42.1  per  cent,  or  all  the  way  from  nearly  the  highest  possible 
figure  down  to  the  lowest  one  obtained  in  the  whole  series  of  tests. 

In  Mr.  Geo.  H.  Barrus's  book  on  Boiler  Tests  there  are  records  of 
a  great  number  of  tests  with  different  kinds  of  boilers,  with  different 
coals,  and  in  different  parts  of  the  country.  Selecting  those  tests  of 
which  complete  records  are  given,  we  find  the  economy  ranges  as  fol- 
lows: 

Water  Evaporated  from  and  at  212°        Number  of  tests  Number  of  tests  Number  of  tests 
per  Ib.  Combustible.  Anthracite.  Semi-bit.  Bituminous. 

over  12  Ibs . .  6 

11. 5  to  12  Ibs 2  6 

11  to  11. 15  Ibs 10  5 

10. 5  to  11  Ibs 20  3 

10  tolO.Slbs 11  5  1 

9      to  10  Ibs 14  6                        2 

8      to    9  Ibs 8  3 

6      to    7  Ibs 1 

66  34  3 

Out'of  66  tests  with  anthracite,  only  two  gave  a  result  over  11.5  Ibs., 
a  figure  which  may  be  reached  with  any  type  of  boiler,  properly  de- 
signed and  set,  by  a  good  fireman  using  good  coal.  Twenty-three  out 
of  the  66  boilers  gave  a  result  below  10  Ibs.,  or  20  per  cent  less  than 
the  highest  figure  attainable.  In  the  semi-bituminous  tests  only  six 
boilers  out  of  34  gave  12  Ibs.,  a  figure  which  may  easily  be  obtained 
with  any  good  form  of  boiler,  properly  proportioned,  properly  set,  and 
properly  fired. 

Spence's  Experiments  on  the  Effect  of  Varying  the  Air-supply.* — 

The  experiments  were  made  in  1887  with  a  "dry-back"  type  of 
marine  boiler,  14  ft.  9  in.  long,  6  ft.  diameter,  with  88  2f  in.  smoke- 
tubes  5  ft.  9  in.  long;  heating  surface,  446  sq.  ft.;  grate-surface,  14.6 
sq.  ft.;  two  internal  furnaces,  with  top  of  grate-bars  1  ft.  3£  in.  from 
crown  of  furnace.  The  experiments  were  all  made  with  the  same 
coal,  fireman,  and  steam-pressure.  The  object  of  the  first  series, 
eleven  tests,  was  gradually  to  increase  the  air-supply  from  12£  Ibs.  per 
pound  of  coal,  an  insufficient  quantity,  to  a  sufficient  quantity  of 
17.3  Ibs.,  10.4  Ibs.  being  theoretically  required  for  complete  combus- 

*  From  Donkin's  "Heat  Efficiency  of  Steam-boilers,"  p.  65.  Original  in  the 
Transactions  of  the  Northeast  Coast  Engineers  and  Shipbuilders,  vol.  4,  1888. 


382 


STEAM-BOILER  ECONOMY. 


tion  of  the  coal.  Other  conditions  were  kept  nearly  constant.  The 
steam-pressure  was  55  Ibs.  The  heating  value  of  the  dry  coal  (New- 
castle nut)  was  13,620  B.T.U.  per  lb.,  and  it  contained  from  1.2  to 
3.5$  ash,  as  shown  by  the  boiler-tests. 

The  first  set  of  experiments  was  made  with  natural  draft.  A 
second  set  of  five  tests  was  made  with  forced  draft,  the  air  per  pound 
of  coal  being  varied  from  17.5  to  23.0  Ibs.;  and  a  third  set  of  eight 
tests,  also  with  forced  draft,  was  made  with  the  grate-bars  lowered  to 
1  ft.  6-|-  in.  below  the  crown-sheet,  with  the  air-supply  from  17.1  to 
22.9  Ibs. 

The  following  are  the  principal  results  obtained : 


Number 
of 
Test. 

Area 
of 
Grate. 
Sq.  Ft. 

Coal  per 
Sq.  Foot 
of  Grate 

Hour. 
Lbs. 

Water  Evaporated 
from  and  at  212°. 

Tempera- 
ture 
of  Gases 
at  End 
of  Boiler. 

Effi- 
ciency.* 
Pei- 
cent. 

Air  per 
Pound 
Fuel. 
Lbs. 

Per  Sq.  Ft. 
of  Heating 
Surface  per 
Hour.—  Lbs. 

Per  Pound 
of  Coal. 
Lbs. 

1  

14.6 

14.6 
14.6 
14.6 
14.6 
14.6 
14.6 
14.6 
14.6 
14.6 
14.6 

17.5 
18.1 
17.8 
18.6 
18.6 
18.8 
18.4 
18.5 
17.0 
17.5 
17.4 

5.27 
5.5 

5.48 
5.74 
5.78 
5.95 
5.85 
6.07 
5.67 
5.93 
5.91 

9.16 
9.26 
9.36 
9.28 
9.46 
9.62 
9.68 
10.01 
10.19 
10.33 
10.25 

779°  F. 
815 
728 
768 
764 
757 
775 
748 
788 
767 
701 

65.0 
65.7 
66.4 
65.8 
67.1 
68.2 
68.6 
71.0 
72.2 
73.2 
72.7 

12.25 
13.1 
13.8 
14.0 
16.8 
16.6 
.    17.3 
18.2 
20.4 
17.3 
18.5 

2  

3       

4  

5  

6  

7  

8 

9  

10  

H  

FORCED-DRAFT   TESTS. 


12.,  

10.1 

42.7 

13  
14  

7.5 
6.38 

40.4 
39.0 

15 

8.25 

31.1 

16  

10.1 

29.8 

FORCED   DRAFT— GRATE-BARS   LOWERED   3   IN. 


8.79 

906 

1100° 

64.7 

18.6 

6.5 

9.57 

919 

67.8 

26.6 

6.6 

y.  15 

944 

64.8 

23.0 

5.4 

9.43 

872 

66.8 

20.7 

6.6 

9.39 

934 

66.6 

17.5 

17  

7.2 

39.5 

6.0 

9.41 

760° 

66.7 

17.1 

18  

7.2 

37.0 

6.4 

10.67 

783 

75  7 

20  3 

19  

7.2 

37.7  , 

6.3 

10.39 

764 

73.6 

20.3 

20  

6.8 

46.3 

7.0 

9.95 

835 

70.5 

22.0 

21 

9  3 

36  3 

7  0 

9.29 

834 

65  9 

20  0 

22  

5.8 

47.5 

6.4 

10.35 

739 

73  4 

21  8 

23  

24 

6.2 

8  2 

36.8 
31.5 

5.4 

5.9 

10.65 

10  27 

741 
692 

75.5 

72  8 

229 

18  0 

*  The  reported  heating  value,  13,620  B.T.U.  per  lb.  dry  coal,  with  from  1.2  to  3.5#  ash.  is 
probably  much  lower  than  the  true  value,  and  the  repoi  ted  efficiencies  are  therefore  probably 
higher  than  the  actual  efficiencies. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


383 


12   13    14   15   16   17   18    19  20  21   22  23  24  25  26  27 
Lbs.Air  per  \b.  Coal. 


The  results  are  plotted  on  the  accompanying  diagram,  Fig.  119. 
Studying  the  diagram  we  see  that  in  the  first  set  of  tests,  those  with 
natural  draft,  there  is  a 
steady  increase  of  efficiency 
as  the  air  per  pound  of  fuel 
increases  from  12^-  to  18 
Ibs.  In  the  second  set,  with 
forced  draft,  and  with  air- 
supply  from  17.5  to  26.6 
Ibs.  all  the  results  are  low, 
due,  no  doubt,  to  the  com- 
bustion being  imperfect  on 
account  of  the  insufficient 
room  in  the  fire-box.  In 

the  third  series  the  air-sup- 

n     £          -  w  .,  FIG.  119. — SPENCE'S  EXPERIMENTS. 

ply  ranges  only  irom  17.1 

to  22.9  Ibs.,  and  the  results  are  erratic,  an  air-supply  of  20  Ibs.  per 
pound  of  coal  giving  both  the  lowest  and  the  highest  efficiency;  or 
65.9  and  75.7  per  cent.  The  difference,  9.8  per  cent,  which  is  13  per 
cent  of  the  higher  figure,  is  not  accounted  for  by  anything  in  the 
record.  The  lower  figure  was  probably  due  to  some  error  in  the  firing. 
The  low  figure  in  the  second  set  of  tests,  64.7  per  cent,  is  partly 
accounted  for  by  the  rate  of  driving  being  much  higher  than  in  the 
other  tests. 

Results  of  Tests  with  Small  Sizes  of  Anthracite  Coal,— The  table 
on  page  384  gives  the  results  of  five  tests  with  small  sizes  of  anthra- 
cite coal  reported  by  Eckley  B.  Coxe  in  Trans.  Am.  Inst.  Mining 
Engineers,  vol.  xxii.  1893.  All  were  made  with  the  Coxe  travelling 
grate,  the  first  four  with  two  Stirling  water-tube  boilers,  and  the  fifth 
with  a  group  of  three  .cylinder  boilers  with  two  mud-drums  under- 
neath, set  over  a  single  furnace,  with  a  cast-iron  water-tube  boiler  in 
the  flue,  containing  nearly  as  much  heating  surface  as  the  cylinder 
boilers.  The  following  remarks  on  these  tests  are  made  by  Mr.  Coxe : 

The  plant  at  Oneida  No.  3  consists  of  two  150-H.P.  Stirling 
boilers  of  the  ordinary  type  to  which  this  grate  has  been  applied.  In 
this  case  a  fire-brick  arch  covers  almost  the  whole  of  the  grate  and  the 
gases  from  the  entire  grate  mingle  at  the  outlet.  The  result  of  having 
this  fire-brick  arch  is  to  keep  up  an  intense  heat  over  the  grate,  giving 
a  chance  for  most  of  the  carbonic  oxide  to  unite  with  the  oxygen  of 
the  free  air  before  the  gases  become  cold  by  contact  with  the  heated 
surface  of  the  boiler.  It  appears  probable  that  it  will  be  an  advantage 


384 


STEAM-BOILER  ECONOMY. 


RESULTS  OF  TESTS   OF  PEA  AND  BUCKWHEAT  WITH  TWO  TYPES 
OF   BOILERS   AND   COXE   TRAVELLING  GRATE. 


1. 

Oneida 
Pea  coal. 

2. 
Oneida 
No.  I 
Buck- 
wheat.j 

3. 
Oneida 
No.  2 
Buck- 
wheat. 

4. 
Oneida 
No.  3 
Buck- 
wheat. 

5. 
Eckley 
No.  3 
Buck- 
wheat. 

KIND  OF  FUEL  USED. 

Pounds  of  water  evaporated   from 
and  at  212°  F.  per  Ib.  dry  coal  
Pounds  of  water  evaporated   from 
and  at  21  2°  F.  per  Ib.  combustible 
Pounds   of   water   evaporated  from 
and  at  212°  F.  per  hour  per  sq.  ft. 

8.56 
10.14 

370 

7.94 
10.06 

3.21 

8.60 
10.57 

3  13 

8.65 
11.12 

3  13 

8.74 
11.10 

3  06 

Pounds  of  coal  per  square  foot  of 

13  63 

13  58 

11  40 

11  34 

q  44 

Average    temperature   of    escaping 

549 

543 

498 

503 

372 

Horse-power  actually  developed.  .  .  . 
Square  feet  beating  surface  per  H.P. 
Percentage  over  rated  capacity.  .... 
Moisture  in  coal  as  fired             . 

372.8 
9.25 
24.26 
2  63 

343 
10.05 
14.33 
4  06 

312.6 
11.03 
4.20 
8  62 

312.8 
11.03 
4.26 
6  53 

165 

11.28 

A  QQ 

Per  cent  of  asli     

15  60 

20  10 

18  71 

22  27 

01   q 

'Oarbon  in  asb  ,  per  cent  

15  85 

12  35 

9  33 

31  90 

oq  cq 

Pressure  of  steam   average 

139  Ibs 

134  lb«? 

1QQ  IHa 

mih«* 

04  \\\a 

"       "   blast,  in.  of  water  
Temperature  of  feed-  water,  average 

ANALYSIS  OF  COAL. 
Water  at  225°  F            

r 

65 
2  15 

jr 

2  00 

r 

62 

2  10 

w 

63 

o  OK 

H" 

68 

2K(\ 

Volatile  combustible  matter  

5  10 

4  90 

5  45 

5  42 

K   f\0 

Ash                   

12  55 

17  35 

15  50 

12  90 

1Q  Q7 

80  20 

75  75 

76  95 

79  63 

78  *>3 

1.620 

1  664 

1  655 

1  642 

I  665 

SIZING  TEST. 
'Chestnut  over  -J"  round  mesh  .  . 

8.44 

| 

.98  i 

Pea  coal  between  |  and  Ty  '  r'd  mesh 
No.  1  buckwheat  betw.  Ty  '  &  f  "    «  ' 

NO.  2      "       ««    t"&Ty  " 

No.  3          «            "    ^"*  A"    " 
Between  JW"  &  yV'   

60.65 
21.70 
3.68 
1.40 
4.13 

6.85 
57.72 
28.74  ' 
2.39 
1.49 

.31 

4.76 
66.57 

19.87 
2  39 

1.50 

4.58 
17.75 
45.95 
19  79 

1.21 
2.60 
31.94 
49.56 
6  31 

Dust    through  y1^"  mesh  (round).... 

1.83 

6.10 

1043 

8  37 

100.00 

100.00 

100.00 

100.00 

100.00 

to  remove  the  heating  surface  of  the  boiler  from  the  combustion- 
chamber  so  that  the  gases  will  not  come  in  contact  with  the  cooler 
iron  surface  until  the  carbonic  oxide  has  been  entirely  burned  and  a 
thorough  mingling  of  all  the  gases  has  taken  place. 

We  have,  we  think,  established  one  fact,  and  that  is  that  the  size 
of  the  coal  does  not  materially  affect  the  number  of  pounds  of  water 


EESULTS  OF  STEAM-BOILER  TRIALS.  385 

evaporated  per  pound  of  combustible.*  It  does  affect  the  number  of 
pounds  of  water  evaporated  per  square  foot  of  heating  surface.  The 
temperature  at  which  the  smaller  coals  burn  is  not  as  great  as  that 
developed  by  the  larger  coal,  and  therefore  1  sq.  ft.  of  heating  surface 
will  not  absorb  as  much  heat  when  we  use  small  coal  as  when  we  use 
large;  but  the  economy  (that  is,  pounds  of  water  evaporated  per 
pound  of  coal)  appears  to  be  about  the  same  in  all  cases.  Of  course, 
the  commercial  value  at  present  of  No.  3  buckwheat  is  very  much 
less  than  that  of  pea  coal. 

Dimensions  and  proportions:  For  tests  Nos.  1,  2,  3,  and  4,  two- 
Stirling  water-tube  boilers.  Each  boiler  4  drums,  viz.,  one  42  ins. 
diam.  and  three  36  ins.,  each  105f  ins.  long;  155  3^-in.  tubes;  heat- 
ing surface  1725  sq.  ft.;  builder's  rating  150  H.P.;  grate  6  ft.  wide 
by  9  ft.  2  ins.  long  =  55  sq.  ft.;  ratio  heating  to  grate-surface  31.4 
to  1.  For  test  No.  5,  cylinder  boilers  with  improved  setting,  consist- 
ing of  3  main  drums  34  ins.  x  36  ft.  and  2  mud-drums  34  ins.  x  20 
ft.  4  ins.  with  8  short  connections,  4  14-in.  and  4  10-in.  diam.;  heat- 
ing surface  of  main  drums  575  sq.  ft.,  of  mud-drums  393  sq.  ft.,  of 
connections  21  sq.  ft.;  together  with  a  cast-iron  water-tube  boiler  in 
the  flue,  with  tubes  2^  ins.  inside  diameter,  heating  surface  873  sq.  ft.; 
total  heating  surface  1862  sq.  ft.  Grate  7  ft.  6  ins.  wide  x  9  ft. 
2  ins.  long  =  68.75  sq.  ft.  Eatio  of  heating  to  grate-surface  27. "* 
to  1. 

Comments  on  the  above  Tests. — It  appears  that  in  test  No.  1,  with 
the  pea  coal,  an  evaporation  of  only  10.14  Ibs.  from  and  at  212°  per 
Ib.  of  combustible  was  obtained,  as  compared  with  11.12  Ibs.  in  test 
No.  4  with  No.  3  buckwheat.  The  more  rapid  rate  of  driving,  3.70 
Ibs.  per  sq.  ft.  of  heating  surface  per  hour  as  compared  with  3.13  Ibs., 
is  not  sufficient  to  account  for  the  difference,  which  is  nearly  10  per 
cent.  The  higher  temperature  ofl  the  escaping  gases,  549°  as  com- 
pared with  503°,  would  account  for  a  loss  of  5  per  cent  if  the  furnace 
temperature  were  2300°  in  both  cases,  but  with  the  same  air-supply 
the  furnace  temperature  should  be  lower  with  the  buckwheat  coal., 
since  it  contained  6.53  per  cent  moisture  while  the  pea  coal  contained 
only  2.63  per  cent,  and  the  buckwheat  coal,  other  conditions  being 
equal,  should  therefore  give  lower  economy  than  the  pea.  It  is  likely 
that  the  low  economy  in  test  No.  1  is  due  to  excessive  air-supply,  and 
that  a  much  higher  result  might  have  been  obtained  if  the  test  had 
been  repeated  with  a  thicker  bed  of  coal  or  with  a  better  regulation 
of  the  air-supply. 

Tests  Nos.  4  and  5  show  a  very  close  agreement,  in  quality  of  coal, 
in  rate  of  burning  and  of  evaporation,  and  in  economy.  The  great 

*  A  different  result  appears  to  have  been  obtained  in  Mr.  Barrus's  tests  with 
Stirling  boilers,  discussed  later. 


386 


STEAM-BOILER  ECONOMY. 


difference  in  these  two  tests  is  in  the  type  of  boiler,  test  No.  4  being 
with  a  Stirling  water-tube  boiler  with  a  fire-brick  arch  furnace,  and 
No.  5  with  a  cylinder  boiler  34  ft.  long  supplemented  by  a  cast-iron 
water-tube  boiler  in  the  flue.  The  advantage  of  the  fire-brick  arch 
in  securing  complete  combustion  of  the  volatile  gases  distilled  from 
the  coal  and  those  formed  by  decomposition  of  its  moisture  is  prob- 
ably equalized  by  the  long  travel  of  the  gases,  34  ft.  under  the 
cylinder  boilers,  which  would  also  tend  to  secure  complete  combustion. 
The  absorptive  capacity  of  the  heating  surface  of  the  two  boilers 
seems  to  be  equal,  confirming  the  statement  that  the  economy  of  a 
boiler  does  not  depend  upon  the  type,  but  upon  the  conditions  under 
which  it  is  operated. 

Tests  of  Stirling  Boilers  with  Anthracite  Coal.*— In  1894  Mr. 
Geo.  H.  Barrus  made  a  series  of  nine  tests  011  two  Stirling  water-tube 
boilers  at  two  collieries  near  Wilkes-Barre,  Pa.  From  the  reports  of 
these  tests  the  table  and  diagram  on  pages  387  and  388  have  been  pre- 
pared. Tests  Nos.  1  and  2  inclusive  were  made  on  a  125-H.P.  boiler  at 
No.  5  shaft  of  the  Lehigh  and  Wilkes-Barre  Coal  Co.,  and  Nos.  8  and  9 
were  made  on  a  150-H.P.  boiler  at  the  Dorrance  colliery  of  the  Lehigh 
Valley  Coal  Co.  The  rating  of  the  boilers  is  on  the  basis  of  11|  sq.  ft. 
of  heating  surface  to  a  horse-power.  Forced  draft  was  supplied  by 
McClave  steam-blowers.  The  coal  used  in  the  several  tests  differed  in 
size  and  quality.  The  sizes  were  determined  by  passing  samples 
through  and  over  screens  of  different  meshes  and  weighing  the  por- 
tions thus  separated.  The  coal  used  in  five  of  the  tests  was  as  follows, 
the  figures  being  given  in  percentages : 


Sizes  of  Screen. 

Over  T6B. 

Through 
iV 

Through 

Through 

135- 

Through 

Test  No.  3.     No.  2  buckwheat  
"     "     6      Culm   No   5  shaft. 

25 

45 
3 

19 
11 

11 

86 

"     "     7      Culm   No.  4  shaft 

18 

24.1 

57.9 

"     "     8      No.  2  buckwheat    .  .  . 

2.5 

65 

32.5 

"     "    9      No  2  buckwheat.. 

10.7 

67 

22.3 

A  Study  of  the  Results  of  the  Stirling  Tests. — For  comparing  the 
results  of  these  tests  they  have  been  plotted  on  the  accompanying 
diagram,  Fig.  120,  showing  the  relation  of  the  water  evaporated  per 
pound  of  combustible,  or  the  economy,  to  the  rate  of  driving,  or  the 


*  From  Mines  and  Minerals,  December,  1897. 


ItESULTS  OF  STEAM-BOILER  TRIALS.  387 

TESTS   OF   STIRLING   BOILERS   AT   ANTHRACITE  COAL-MINES. 


Number  of  Test.         ....          

1 

2 

3 

4 

5 

Test  for  capacity  or  economy  

Capacity. 

Buck- 
wheat. 

Capacity. 

Culm  i, 
Buck- 
wheat £. 

Economy. 

Economy. 

Capacity. 

Buck- 
wheat. 

Buck- 
wheat. 

Buck- 
wheat. 

Ash  and  clinker  per  cent  .  .    . 

12.0 
45 
31.9 
.16 
1.00 

12  9 

25.9 
45 
31.9 
.16 
1.00 

12.0 
45 
31.9 
.16 
0.20 

7.2 

13.17 
3.61 

172.8 
38.2 

500 
9.955 
11.324 

12.0 
38 

37.8 
.16 
0.00 

6.7 

14.84 
3.33 

159.6 

27.7 

485 
10.075 
11.449 

12.6 
38 
37.8 
.16 
1.00 

13.3 

28.28 
6.06 

290.2 
132 

684 
9.310 
10.052 

Ratioofgratetolieatingsurface,  1  to 
Draft-suction  in  stack,  ins.  of  water 
Draft-pressure  in  asli-pit   ins 

Steam  used   to  run  blowers,  esti- 
mated H.P  

Coal  burned  per  hour  per  square 
foot  of  grate    Ibs            

29.3 
6.04 

289.3 
131 

800 
7.563 
8.594 

14.55 
2.74 

131.3 
5.0 

439 
6.910 
9.325 

Water   evaporated   per    hour   per 
square  foot  heating  surface,  Ibs. 
Horse-power  developed    H  P 

H.P.  above  boiler's  rating,  per  cent 
Average  temperature  of  flue-gases, 
degrees  F.  about  

Water  evaporated  from  and  at  212° 
per  pound  of  coal    Ibs    .  .  . 

Water  evaporated  from  and  at  212° 
per  pound  of  combustible  

Number  of  Test  

6 

7 

8 

9 

Test  for  capacity  or  economy 

Capacity. 

Capacity. 

Capacity. 

Economy. 

Culm  No.  5. 

Culm  No.  4. 

Buckwheat. 

Buckwheat. 

Ash  and  clinker,  per  cent  

15.1 
45 
31.9 
.16 
0.90 

8.7 

10.66 

2.81 

134.8 

7.8 

462 
9.122 
10.745 

20.7 
45 
31.9 
.16 
1.00 

12.3 

17.63 
3.79 

181.6 
45.3 

543 

7.889 
9.949 

15.6 
47.3 
36.5 
.12 
1.50 

13.2 

23.82 
4.8 

275.9 
83.9 

560 
8.437 
9.996 

13.9 
47.3 
36.5 
.10 

0.87 

Ratio  of  grate  to  heating  surface,  1  to 
Draft-suction  in  stack,  ins.  of  water 
Draft-pressure  in  ash-pit,  ins  
Steam  used  to   run  blowers,  esti- 
mated H.P  

Coal  burned  per  hour  per  square 
foot  of  grate,  Ibs  

18.16 
3.92 

225.2 
50.1 

524 
9.046 
10.495 

Water   evaporated   per    hour   per 
square  foot  heating  surface,  Ibs.. 
Horse-power  developed,  H.P  
H.P.  above  boiler's  rating,  percent 
Average  temperature  of  flue-gases, 

Water  evaporated  from  and  at  212° 
per  pound  of  coal    Ibs    .... 

Water  evaporated  from  and  at  212° 
per  pound  of  combustible  

388 


STEAM-BOILER  ECONOMY. 


water  evaporated  per  square  foot  of  heating  surface  per  hour.  For 
further  comparison  there  are  also  plotted. two  dotted  lines  represent- 
ing the  maximum  and  the  average  results  of  tests  with  anthracite 
coal  given  in  Mr.  Barrus's  book  011 "  Boiler-tests,"  together  with  a  line 
representing  the  maximum  results  obtained  in  the  boiler-tests  at  the 
Centennial  Exhibition.  As  the  Centennial  tests  were  made  with  egg 
coal  of  excellent  quality  and  under  the  most  favorable  conditions,  it  is  to 
be  expected  that  their  maximum  results  will  be  considerably  above  tnose 
obtained  with  buckwheat  coal.  Of  the  tests  with  buckwheat  coal 
given  in  the  above  table,  Nos.  3,  4,  and  5  lie  close  to  the  line  of 
Mr.  Barrus's  maximum  results,  Nos.  8  and  9  are  near  the  line  of  his, 


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4 
ft.  of  Heating-  Surface  per  Hour. 


FIG.  120. — TESTS  OP  STIRLING  BOILERS  WITH  ANTHRACITE  BUCKWHEAT  ANI> 
CULM  COMPARED  WITH  TESTS  RECORDED  IN  BARRUS  ON  "BOILER-TESTS" 
AND  WITH  THE  CENTENNIAL  TESTS. 

average  results,  and  No.  1  is  considerably  below  the  average  line.  Of 
the  tests  with  culm,  No.  6  is  a  little,  and  No.  7  considerably,  below 
the  average  line,  while  test  No.  2,  with  one-fourth  buckwheat  and 
three-fourths  culm,  is  far  below  the  average  line.  In  explanation  of 
these  varied  results  we  find  on  referring  to  Mr.  Barrus's  report  that 
in  tests  Nos.  1,  2,  and  3  the  shaking  grate-bars  had  their  air-spaces 
unevenly  adjusted,  causing  an  uneven  distribution  of  air  through  the 
bed  of  coal.  This  may  account  to  some  extent  for  the  low  results  of 
tests  Nos.  1  and  2,  but  it  does  not  seem  to  have  had  much  effect  in 
test  No.  3,  the  result  of  which  is  very  high.  The  three  tests  were 
made  on  three  consecutive  days,  and  possibly  in  test  No.  1  the  firing 


RESULTS  OF  STEAM-BOILER  TRIALS.  389 

was  done  unskilfully,  for  the  temperature  of  the  gases  was  beyond  the 
range  of  the  thermometer,  or  over  800°,  and  during  the  whole  run  the 
flame  from  the  coal  extended  into  the  stack  and  during  part  of  the 
time  flame  could  be  seen  issuing  from  the  top  of  the  stack.  Over- 
driving of  the  boiler  does  not  sufficiently  account  for  this,  for  in  test 
No.  5  with  the  same  coal  (or  nearly  the  same)  as  in  No.  1  and  with 
the  boiler  developing  as  great  a  horse-power  the  temperature  of  the 
flue-gases  averaged  only  684°.  Test'  No.  2,  with  three-fourths  culm 
and  one-fourth  buckwheat,  gave  a  result  over  12  per  cent  below  test 
No.  6,  all  culm,  the  boiler  in  the  two  tests  being  driven  at  the  same 
rate.  This  loss  of  12  per  cent  may  have  been  due  to  mal-adjustment 
of  the  grate-bars,  but  it  was  probably  partly  due  to  the  mixing  of  two 
kinds  of  coal,  which  is  generally  believed  to  give  poor  results  with 
anthracite  coal,  the  fine  sizes  choking  up  the  interstices  between  the 
larger  sizes,  and  doing  this  irregularly  on  different  portions  of  the 
grate,  causing  irregular  burning,  with  excess  of  air-supply  through 
some  portions  and  deficient  supply  through  others. 

Tests  Nos.  1  and  5,  with  the  same  coal  and  the  same  rate  of  driv- 
ing of  the  boiler,  show  a  remarkable  difference  of  economy,  the  former 
being  over  14  per  cent  below  the  latter.  The  differences  of  the  con- 
ditions of  these  tests  which  may  have  caused  the  difference  in  results 
were:  (1)  Larger  grate-surface  in  No.  1  than  in  No.  5;  (2)  bad 
adjustment  of  the  air-spaces  in  No.  1 ;  (3)  possibly,  unskilled  firing  in 
No.  1.  The  larger  grate-surface  in  No.  1  is  not  likely  to  have  been 
the  cause,  for  test  No.  3  with  the  same  large  grate-surface  gave  prac- 
tically as  high  a  result  as  No.  4,  with  the  reduced  grate-surface.  The 
difference  in  tests  Nos.  1  and  5  is  instructive  in  showing  what  a  wide 
difference  in  results  is  possible  in  the  same  boiler,  with  the  same  coal 
and  the  same  rate  of  driving,  due  to  what  may  appear  to  be  slight 
causes,  such  as  difference  in  the  air-spaces  through  the  grate-bars  or 
in  the  skill  of  the  firemen. 

Tests  Nos.  8  and  9  fall  considerably  below  the  line  of  tests  Nos. 
3,  4,  and  5.  These  tests  were  made  on  a  different  boiler  of  the  same 
make,  but  there  was  probably  not  any  difference  in  the  details  of  con- 
struction of  the  boiler  or  setting  which  would  account  for  the  differ- 
ence in  results.  There  was,  however,  considerable  difference  in  the 
coal,  as  shown  by  the  percentage  of  ash  and  by  the  table  of  sizes. 
The  coal  used  in  Nos.  8  and  9  was  finer  in  size  than  that  used  in  test 
No.  3,  66  per  cent  of  it  going  through  a  £-in.  screen,  while  in  the  coal 
of  test  No.  3  only  30  per  cent  went  through  %  in.  The  coal  of  tests 


390  STEAM-BOILER  ECONOMY. 

Nos.  8  and  9  was  of  an  intermediate  size  between  that  of  test  No.  3 
and  culm,  and  the  diagram  shows  that  the  results  given  by  it  are  also 
intermediate  between  those  of  the  other  coals. 

The  results  plotted  in  the  diagram  are  the  pounds  of  water  evap- 
orated per  pound  of  combustible  and  not  per  pound  of  coal.  Since 
the  combustible  of  all  the  coals  used  in  these  tests  is  practically  of 
identical  quality,  it  might  be  expected  that  all  the  coals  would  give 
the  same  result  per  pound  of  combustible,  and  that  results  per  pound 
of  coal  would  correspond,  except  as  they  are  influenced  by  different 
percentages  of  moisture  and  ash.  The  plotted  results  show,  however, 
that  although  the  combustible  portion  of  all  the  coals  may  be  identical 
in  quality,  it  gives  different  results  when  it  is  contained  in  coal  of 
different  sizes.  Tests  Nos.  3,  4,  and  5,  with  the  largest  size  of  buck- 
wheat coal,  give  the  best  results,  test  Nos.  8  and  9  with  finer-sized 
buckwheat  give  results  much  lower,  and  tests  Nos.  6  and  7,  with 
culm,  still  lower  results.  Tests  Nos.  1  and  2,  both  exceptionally  low, 
may  be  neglected  from  the  comparison,  as  they  were  influenced  by 
unfavorable  conditions,  such  as  mixing  of  sizes  and  uneven  adjustment 
of  the  air-spaces.  The  best  results  obtained  with  the  large-sized 
buckwheat  coal,  also,  are  from  5  to  7  per  cent  below  the  best  results 
obtained  in  the  Centennial  tests  with  egg  coal. 

A  reasonable  theory  to  account  for  the  regular  decrease  in  evap- 
oration per  pound  of  combustible  as  the  size  of  the  coal  is  made  finer 
seems  to  be  the  following :  When  egg  or  other  large-sized  coal  is  used, 
a  thick  bed  of  it  is  carried  on  the  grate,  through  which  the  air  passes 
with  comparative  uniformity.  The  lumps  of  coal  burn  away  slowly, 
from  the  surface ;  fresh  coal  is  fired  at  long  intervals  of  time,  and  the 
condition  of  the  fire  is  always  nearly  the  same.  If  the  draft  and  the 
thickness  of  the  bed  are  properly  related  to  each  other,  and  the  boiler 
is  well  designed,  the  maximum  economy  possible  with  the  coal  may 
be  obtained.  With  finer-sized  coals,  however,  a  thinner  bed  must  be 
carried,  relatively  to  the  force  of  draft ;  air-holes  are  more  likely  to  be 
formed  in  the  bed,  causing  too  great  a  supply  of  air  to  pass  through 
some  portions  while  an  insufficient  supply  is  furnished  to  other  por- 
tions. Fresh  coal  is  fired  at  frequent  intervals,  involving  frequent 
openings  of  the  doors  and  inrush  of  cold  air;  and  the  fresh  coal  for  a 
short  time  after  firing,  being  small  in  size,  is  apt  to  clog  the  fire  and 
obstruct  the  air-supply,  causing  the1  burning  of  the  coal  to  carbonic 
oxide  instead  of  carbonic  acid.  The  bed  of  coal  being  thin  and  the 
draft  strong,  if  the  fireman  leaves  the  fire  unattended  to  for  a  minute 


RESULTS  OF  STEAM-BOILER  TRIALS. 


391 


or  two  after  it  is  time  to  fire  fresh  coal,  air-holes  will  form  rapidly, 
while  with  egg  coal  a  period  of  five  minutes  makes  but  little  differ- 
ence. 

Mr.  Barrus  gives  in  his  reports  of  these  tests  a  statement  of  the 
"  efficiency,"  or  ratio  of  the  heat  absorbed  by  the  boiler  to  the  heating 
value  of  the  coal,  in  the  several  economy  tests,  as  follows : 


Test  No. 

4 

6 

7 

9 

Coal. 

Buck- 
wheat. 

Culm 
No.  5. 

Culm 
No.  4. 

Buck- 
wheat. 

1.  Heating  value  of  coal  per  Ib.  of  com- 
bustible  BTU  

13  877 

13,985 

14  044 

14  157 

2.  Water  evaporation  from  and  at  212°  per 
Ib    combustible    Ibs 

11  449 

10  745 

9  949 

10  495 

3.  Heat  utilized  (line  2  X  966)  B.T.U  
4.  Efficiency  (line  3  —  line  1)  

11,080 
79  6 

10,360 

74.2 

9,611 
68.4 

10,138 
71.6 

The  maximum  range  of  variation  of  the  heating  values  of  the  four 
coals  is  only  270  B.T.U.  per  pound,  or  less  than  2  per  cent.  It  is 
probable  that  all  of  these  heating  values  are  too  low,  due  to  imperfec- 
tion of  the  calorimeter  by  which  they  were  determined,  or  possibly  to 
the  fact  that  the  samples  used,  were  not  thoroughly  dry  (the  heating 
value  of  anthracite  calculated  from  the  analysis  is  usually  about 
14,80.0  B.T.U.  per  pound  of  combustible),  and  that  the  efficiencies 
recorded  are  consequently  too  high,  but  the  figures  give  relative  values 
which  may  be  accepted  as  correct.  The  reported  efficiency  in  test 
No.  4  is  79.6  per  cent  and  that  in  No.  7  only  68.4  per  cent,  although 
the  boiler  was  driven  at  practically  the  same  rate  in  the  two  tests. 
The  falling  off  in  efficiency  of  (79.6  —  68.4)  -f-  79.6,  over  14  per  cent, 
shows  how  much  poorer  a  fuel  practically  the  culm  is  than  buckwheat, 
per  pound  of  combustible,  although  the  combustible  itself  in  the  two 
coals  is  of  identical  quality.  The  practical  value  of  culm  per  pound 
of  coal  is  further  reduced  by  the  greater  percentage  of  ash  and  moist- 
ure it  usually  contains,  as  compared  with  buckwheat. 

The  results  of  these  tests  show  that  the  efficiency  of  any  given 
steam-boiler  is  not  a  constant  quantity,  that  it  varies  not  only  with 
the  rate  of  driving,  but  with  the  quality  of  the  coal  and  even  with  the 
size  of  coal  of  the  same  quality. 

Another  useful  lesson  to  be  learned  from  these  tests  is  in  regard 
to  the  capacity.  The  three  capacity-tests  with  buckwheat  coal, 
Nos.  1,  5,  and  8,  gave  a  horse-power,  respectively,  131,  132,  and  84: 


392 


STEAM-BOILER  ECONOMY. 


per  cent  above  the  rated  power  of  the  boiler,  and  the  highest  economy 
was  obtained  when  the  boiler  was  driven  28  per  cent  above  its  rating. 
Whether  any  higher  economy  could  have  been  obtained  with  this  coal 
if  the  boiler  had  been  driven  at  a  lower  rate  cannot  be  said,  for  no 
test  was  made  at  a  lower  rate  with  buckwheat  coal.  The  three 
capacity-tests  with  culm,  Nos.  4,  6,  and  7,  gave  -respectively  5,  8,  and 
45  per  cent  above  rating,  although  the  force  of  draft  was  practically 
the  same  as  in  the  tests  with  buckwheat  coal.  It  appears  then  that 
a  boiler  will  not  develop  the  same  horse-power  from  culm  as  from 
buckwheat  unless  the  grate-surface  or  the  draft,  or  both,  are  increased. 
Comparative  Trials  on  Three  Two-flue  Boilers  with  Pittsburg 
Coal. — These  tests  were  made  by  the  Shoenberger  Steel  Co.,  Pittsburg, 
Pa.,  in  1897,  to  determine  the  efficiency  of  the  American  Underfeed 
Stoker  as  compared  with  flat  grates  when  applied  to  two-flue  boilers.  ' 

Grate-surface,  total  of  three  boilers,  90 sq.  ft.;  water-lieating  surface,  1225  sq.  ft.; 
ratio  of  heating  to  grate-surface,  13.6. 


Americar 

i  Stoker. 

Economy. 

Capacity. 

Duration   hours      

8 

8 

7 

101.2 

101.09 

99.24 

Temperature  of  escaping  gases,  °F  
"            "  feed  water,  °F    

816.3 
1499 

735.1 
155.9 

828 
171.3 

Run  of  Mine 

River  Slack 

River  Slack 

Quantity  of  coal  consumed,  pounds  

13,500 
12 

10,500 
9.49 

12,300 

Coal  per  square  foot  of  grate  per  hour,  Ibs. 
Total  water  actually  evaporated,  pounds. 
Water  per  hour,  equivalent  from  and  at 
212°  F    pounds.  

18.7 
82,160 

11,344 

14.5 
92,140 

12,653 

19.4 
100,917 

15,600.3 

Water  per  hour,  per  square  foot  heating 

926 

1033 

12.73 

Evaporation,  apparent  per  Ib.  of  coal,  Ibs. 
Evaporation,  from  and  at  212°  F.,  Ibs...  . 

6.086 
6  72 
327  8 

8.775 
9.64O 

360.7 

8.204 
8.877 

452 

120 

120 

120 

Ratio  of  H.P.  developed   to    builders' 

2.73 

3.05 

3.7 

Heating  surface  per  horse-power,  sq.  ft. 
Per  cent  increase  of  capacity  by  the  use 

3.72 

3.34 
11  6 

2.7 
37.5 

Per  cent  increase  evaporation  per  pound 
of  coal    as    shown   by  the   American 

44  5 

32 

Efficiency  assuming  the    heating    value 
per  Ib.  combustible  at  15,000  B.T.U., 

433 

62.1 

57  2 

RESULTS  OF  STEAM-BOILER  TRIALS.  393 

The  results  of  these  tests  are  of  interest  for  many  reasons.  The 
hand-fired  test  is  fairly  representative  of  what  was  every-day  practice 
with  the  two-flue  boiler  in  the  Pittsburg  iron-mills  until  the  general 
introduction  of  water-tube  boilers  and  improved  furnaces  and  methods 
of  firing.  In  this  test  the  boiler  was  driven  at  2.73  times  its  rated 
power,  the  flue-gases  escaped  at  816°  F.,  and  the  calculated  efficiency 
is  only  43.3  per  cent.  In  the  "economy"  test,  so-called,  with  the 
stoker,  the  boiler  was  driven  at  a  still  higher  rate  of  evaporation,  viz., 
3.05  times  its  rated  power,  although  less  coal  was  burned  under  it,  the 
temperature  of  the  flue-gases  was  only  735°,  and  the  efficiency  was 
brought  up  to  62.1°.  This  is  a  very  high  efficiency  for  such  a  rate  of 
driving,  but  it  could  110  doubt  have  been  brought  up  to  72  per  cent  if 
the  rate  of  driving  had  been  reduced  about  half  and  the  temperature 
of  the  gases  had  thereby  been  reduced  to  below  500°.  In  the 
capacity-test  with  the  stoker,  still  more  coal  per  hour  was  burned  than 
in  the  hand-fired  test,  and  the  rate  of  driving  was  the  extraordinary 
figure  of  12.73  Ibs.  from  and  at  212°  per  sq.  ft.  of  heating  surface  per 
hour,  or  3.7  times  the  rated  power,  yet  the  temperature  of  the  flue- 
gases,  828°,  was  only  a  trifle  higher  than  in  the  hand-fired  test,  while' 
the  efficiency,  57.2  per  cent,  was  very  much  higher.  The  results  of 
the  test  show  the  advantage  gained  by  the  short  flame  of  very  high 
temperature  produced  by  the  American  stoker  with  its  forced  blast, 
over  the  long  smoky  flame  of  comparatively  low  temperature  produced 
in  the  ordinary  furnace  by  hand-firing  and  natural  draft. 

Applying  to  the  results  of  these  tests  the  "criterion"  formula 
given  in  the  chapter  011  Efficiency  of  Heating  Surface,  page  221,  viz., 

K-  4.8^  23.04      IP 

"  ~  '' 


966(1  +  O.LS/  W~  '    (A'  -4.80    #' 

we  obtain,  taking  JTas  15,000 

for          W/S=9.%Q  10.33  12.73 

Ea  =  §.n  9.64  8.877 

a=   457  244  234 

The  last  two  values  of  a,  244  and  234,  represent  excellent  perform- 
ance. The  high  value  of  a,  457,  represents  poor  performance,  which 
is  accounted  for  by  incomplete  combustion  due  to  an  unsuitable 
furnace. 

Test  of  One  of  the  Babcock  &  Wilcox  Boilers  for  the  IT.  S.  Cruiser 
"Cincinnati."  —  In  the  Annual  Report  of  the  Chief  of  Bureau  of  Steam 
Engineering,  for  1900,  there  is  published  a  report  of  a  test  made  on 


394  STEAM-BOILED  ECONOMY. 

one  of  the  new  boilers  built  by  the  Babcock  &  Wilcox  Company  for  the 
Cincinnati,  by  a  board  composed  of  Lieutenant  Commander  A.  B. 
Willits  and  Lieutenant  B.  C.  Bryan,  U.  S.  Navy.  This  test  was  made 
June  15  to  22,  1900,  at  the  works  of  the  builders,  Elizabethport,  X.  J., 
and  the  following  synopsis  includes  the  most  important  data  obtained : 

Description  of  Boiler  and  Appurtenances. — The  boiler  is  com- 
posed entirely  of  wrought  steel,  the  point  of  difference  between  it  and 
the  older  type  of  this  make  of  boiler  being  in  the  arrangement  of 
baffle-plates  (as  shown  in  the  sectional  view,  Fig.  106,  p.  276),  which 
compel  the  products  of  combustion  to  pass  three  times  across  the 
tubes  before  entering  the  uptake.  The  small  tubes  are  2  ins.  outside 
diameter,  while  the  bottom  tube  in  each  section  or  element  is  4  ins. 
outside  diameter. 

BOILER  DATA. 

Diameter  of  top  drum,  42  ins.  (inside). 

Length  of  top  drum,  .12  ft. 

Tubes  :    Number,  526  ;    2  ins.  outside  diameter  ;    length,  8  ft.     Also  40  ;    4  ins. 
outside  diameter  ;  length,  8  ft.  5f  ins. 

Grate-surface  :  Length,  6  ft.  8£  ins.;  width,  9  ft.  5|  ins.;  area,  63.25  sq.  ft. 

Grate-surface  reduced  to  5  ft.  6  ins.  length,  52  sq.  ft.  area,  in  tests  Nos.  5  and  6. 

Heating  surface  :  Area,  2640  sq.  ft.;  ratio  to  grate,  41.74  :  I. 

Smoke-pipe  :  Area,  7.876  ft. ;    height,  48  ft.  above  grate  ;  ratio  to  grate,  1 :  8.03. 

Weight  of  boiler  and  all  fittings  except  uptakes  and  smoke-pipe  : 

Without  water,  Ibs 53,304 

With  water,  5  ins.  in  glass ;  steam  at  215  Ibs.,  Ibs 62,802 

Total  weight  per  sq.  ft  of  grate-surface,  Ibs 992.9 

Total  weight  per  sq.  ft.  of  heating  surface,  Ibs 23. 79 

Weight  of  air-heater  and  ducts, *lbs 5,320 

Blower  fan  :  Sturtevant ;  diameter,  60  ins. ;  driven  by  belt  from  shop  engines. 

Area  of  blower  inlet,  9.62  sq.  ft.;  outlet,  6.89  sq.  ft. 

Air-heater  :  Two-pass  ;  3  in.  tubes.     Area  of  surface,  495  sq.  ft. 

The  boiler  was  erected  in  a  wooden  structure  built  especially  for 
the  test  and  having  the  following  dimensions  :  Length,  29  ft.  2  ins. ; 
width,  17  ft.  2-j-  ins. ;  height,  21  ft.  This  was  made  as  nearly  air- 
tight as  possible,  but  contained  several  windows  that  could  be  opened 
or  closed  to  regulate  the  amount  of  draft-pressure.  The  blower  was 
driven  by  belting  from  the  main  shop  engines  and  ran  continually. 
The  air-heater  consisted  of  210  3-inch  tubes  3  ft.  long,  spaced  4  ins. 
from  centre  to  centre  one  way,  and  5  ins.  the  other  way.  A  vertical 
division-plate  divided  the  tubes  into  two  separate  sets  or  nests,  and  a 
horizontal  baffle-plate  extended  across  from  the  outside  of  each  nest  to 
within  12  ins.  of  the  division-plate.  When  the  heater  was  in  use,  the 
air  from  the  air-tight  fire-room  entered  at  the  top,  passed  once  across 
the  tubes  over  the  baffle-plate,  and  back  under  same  to  outlets  leading 
to  back  of  ash-pit,  the  front  ash-pit  doors  being  closed.  When  the 
air-heater  was  not  to  be  used,  the  gases  were  by-passed  by  a  damper, 
and  the  air  entered  the  ash-pit  through  the  front,  the  doors  thereto 
being  removed. 


RESULTS  OF  STEAM-BOILER  TRIALS.  395 

Description  and  Object  of  Tests. — Seven  tests  were  made  in  all.  Six 
of  these  consisted  of  three  pairs  in  which  the  two  tests  of  each  pair 
were  under  similar  conditions  in  every  way  except  that  of  using  the 
air-heater,  one  being  with  and  the  other  being  without  this  heater,  in 
order  to  define  the  economy  due  to  its  use.  The  last  or  seventh  test 
was  for  the  maximum  consumption,  and  was  made  without  the  air- 
heater  and  with  full  grate.  Two  pairs  of  tests,  one  at  a  consumption 
of  about  20  Ibs.  of  coal  and  the  other  at  about  35  Ibs.  of  coal  per  square 
foot  of  grate  per  hour,  were  made  with  the  full  grate  service  in  use, 
These  tests  will  be  found  in  tables  of  results  numbered  1,  2H,  3H,  4. 
the  letter  H  signifying  that  the  air-heater  was  in  use  during  the  tests. 
Tests  1  and  2H  were  of  eight  hours'  duration,  and  tests  3H  and  4  were 
of  six  hours'  duration.  The  grate-surface  was  then  reduced  to  52  sq. 
ft.  by  a  course  and  a  half  of  bricks,  seven  courses  in  height,  at  back 
of  furnace,  and  tests  Nos.  5  and  6H,  lasting  four  hours  each,  were 
ma$e,  burning  about  50  Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour.  The 
bricks  were  then  removed  from  the  furnace  and  test  No.  7,  lasting 
three  and  one-third  hours,  was  made,  burning  nearly  60  Ibs.  of  coal 
per  sq.  ft.  of  grate  per  hour.  The  data  and  resul-ts  of  these  tests  will 
be  found  in  the  accompanying  tables. 

Coal  and  Firing. — The  coal  used  was  Pocahontas  coal  from  Flat 
Top  Mine.  It  contained  considerable  slate  and  clinkered  badly.  On 
tests  Nos.  1  and  2H  run-of-mine  coal  was  used;  on  tests  Nos.  3H,  4,  5, 
and  6H  the  coal  was  screened,  using  a  screen  with  a  1-inch  mesh.  On 
test  No.  7  the  screenings  from  the  former  tests  were  run  over  a  f-inch 
mesh  screen,  and  the  coal  thus  screened  was  mixed  with  the  screened 
coal  used  in  ofher  tests.  The  firing  was  good  and  very  regular.  Two 
alternate  doors  were  fired  in  rapid  succession.  The  other  two  sections 
of  fires,  in  wake  of  the  other  two  doors,  were  then  levelled  with  a  hoe, 
then  sliced  through  the  slicing  door,  and  then  coaled,  the  average 
time  between  coalings  of  the  same  two  furnaces  being  from  eight  to 
ten  minutes.  The  furnace  doors  were  open  about  twenty-five  seconds 
when  coaling  and  about  ten  seconds  in  levelling.  The  coal  made  com- 
paratively little  smoke  except  when  firing  or  working  fires.  The  data 
in  regard  to  smoke  were  taken  by  using  Eingelmann  charts. 

Description  of  Apparatus. — The  water  was  weighed  in  two  tanks, 
each  supported  on  a  platform  scale,  and  run  into  a  third  tank  below, 
from  which  the  feed-pumps  drew  water.  All  pipes  were  above  ground 
and  in  plain  sight,  and  wherever  connected  to  other  piping  or  boilers, 
plugs  were  left  out  of  T  connections  to  show  that  there  was  no  leakage. 
The  gross  and  tare  of  each  tank  was  taken,  and  the  temperature  was 
taken  at  the  lower  tank  just  as  each  upper  tank  drained  into  it.  The 
feed-water  was  heated  by  steam  injection  before  entering  the  weighing- 
tanks. 

The  coal  was  weighed  in  barrows  on  platform  scales  in  the  fire-room 
and  dumped  on  the  floor.  The  time  was  taken  when  each  lot  of  bar- 
rows were  fired. 

A  sample  shovelful  of  coal  was  taken  from  each  lot  of  barrows  and 
thrown  into  a  barrel,  and  from  this,  mixed  and  quartered,  the  final 
samples  for  analyses,  calorimeter  and  moisture  determinations  were 


396 


STEAM-BOILER  ECONOMY. 


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RESULTS  OF  STEAM-BOILER   TRIALS. 


39T 


ANALYSES   OF  WASTE  GASES  MADE  DURING  TESTS   OF   U.   S.   S. 
"CINCINNATI"  BOILER,  ELIZABETHPORT,  N.  J.,  JUNE,  1900. 


Date. 

'  1900. 

June  15-( 
I 

June  16« 

r 

June  18-i 
I 

I 

June  19«{ 
I 

r 

June  20«| 

( 

June  21  <{ 

I 

June  23 

r 

June  25  X 

1 
Time. 

Condition  of  fire  when  sample  was  taken. 

CO" 

0 

CO 

'ounds  dry 
gas  pei- 
Pound 
Carbon. 

I 
J-    16.8 

1 

1 
-     19.1 

1 
>•    17.3 

J 

1 

[     18.8 

I 

I    20.6 

J 

j.    17.3 
.     18.6 

1,  • 

}.     18.5 
J 

4.58 
5.15 
5.30 
5.55 
6.16 
6.27 
7.05 

11.45 
12.50 
1.50 
3.50 

11.25 
12.40 
12.50 
12.58 
1.03 

10.10 
10.25 

10.28 
10.35 
11.00 

2.20 

2.40 

10.25 
11.00 
11.04 
11.13 
12.25 
12.36 

11.00 
11.03 
11.18 
11.50 
11.55 
11.59 

11.21 
11.45 
12.38 
2.26 
2.30 
2.43 

10  16 
10.  21 
11.10 
11.13 
11.47 

15.2 
14.3 
13.0 
12.5 
14.3 
12.7 

16.0 
14.0 

3.3 
3.0 
6.5 
6.7 
3.7 
6.6 

2.0 
4.5 

1.0 
2.0 
0.0 
0.8 
1.0 
0.7 

2.0 
1.1 

Just  before  firing               

Just  after'  raking                      

Three  minutes  after  raking  and  just  be- 

Average  

13.4 
12.0 
12.0 

6.4 
5.0 
6.6 

4.8 

5.7 

0.0 
1.0 
0.2 
0.7 

0.5 

Just  after  slicing        

Just  after  slicing        .... 

13.2 
12.7 

Average  

One-half  minute  after  firing 

12.3 
14.2 
12.5 
13.0 
13.5 

13.1 

3.4 
4.0 
4.3 
4.0 
5.4 

2.7 
0.1 
1.2 
3.4 
0.2 

While  slicing        

Just  after  slicing        ....         .  .            .... 

Just  before  slicing  

One  minute  after  firing  

Average  

4.2 

1.5 

While  slicing            .   . 

15.0 

13.8 
14.4 
13.2 

13.0 
10.2 
10.2 

12.8 

3.2 

5.2 
3.1 
5.6 

5.6 
8.3 
9.0 

5.7 

1.2 

0.6 
0.9 
0.4 

0.6 
0.5 
0.3 

~0.~6~ 

While  slicing  (all  samples  except  1  1  o'clock 
collected  through  i-inch  iron  pipe),  .  .  . 

One  minute  before  firing.  .  .  . 

While  slicing  (sample  collected  through 
glass  tube)  

Just  after  raking 

While  slicing 

i3.5 
11.2 
10.4 
9.2 
12.1 
14.2 

11.8 

5.7 
8.4 
8.1 
9.9 
5.4 
4.0 

6.9 

d.O 

0.3 
0.5 
0.0 
0.7 
0.8 

0.4 

While  slicing        

Just  after  firing  

Two  minutes  before  raking               .... 

Just  after  raking  .... 

Average  ........ 

Just  after  raking  

15  7 

4.6 
6.0 
3.0 
5.6 
5.3 
4.2 

4.8 

0.1 
0.0 
0.6 

0.1 
0.4 
0.0 

0.2 

13.0 
15.4 
18.6 
18.0 
16.0 

14.5 

Just  after  firing        

Just  after  raking    .  .  . 

One  minute  before  raking  .... 

Just  before  raking 

Average.  . 

Two  minutes  before  firing 

14.3 
11.0 

4.2 

9.0 

"  f.9* 
4.2 

3.8 

5.8 

1.1 

00 

o!4' 

1.0 
1.0 

0.7 

Two  minutes  before  firing.  .  . 

Just  before  levelling  and  firing 

Just  after  firing  

11.8 
13.3 
14.2 

i27<r 

Just  after  firing 

Two  minutes  before  firing  

A  vera  ge        .  .  . 

15  3 

4.1 

6.0 
6.6 
5.2 

11.2 

6.6 

1.0 
1.0 
0.3 
0.8 
0.3 

0.7 

One  minute  before  firing     , 

13.0 
13.7 
14.0 
9.0 

13.0 

Just  after  levelling 

Just  after  firing  .  .     .  . 

Just  after  firing.  ...                

Average  

398 


STEAM-BOILER  ECONOMY. 


taken.  The  gases  for  analyses  were  drawn  from  near  the  centre  of  the 
base  of  smoke-pipe  by  means  of  a  pipe  inserted  therein  connected  with 
an  aspirator  and  small  Orsat  instrument. 

All  draft-pressures  were  taken  outside  the  building,  pipes  being  led 
there  from  the  different  places  where  pressure  determinations  were 
required. 

Temperatures  were  taken  at  the  back  and  front  of  uptake  just 
above  the  heater;  in  front  by  a  mercurial  pyrometer,  and  at  the  back 
by  a  metallic  pyrometer.  When  the  air-heater  was  used  the  tempera- 
ture was  taken  in  addition  just  below  the  heater  by  means  of  a  mer- 
curial pyrometer. 

The  moisture  in  the  steam  was  determined  by  a  Barrus  universal 
calorimeter.  The  steam  was  found  practically  dry  in  all  cases.  The 
steam  was  partly  used  in  the  shop  and  partly  blown  off  into  the  atmos- 
phere, the  pressure  being  controlled  by  regulating  a  small  stop-valve 
by  hand. 

Measurement  of  Water  in  Boiler,  and  Time  of  Getting  Up  Steam. — 
Before  making  test  No.  6H,  on  June  21,  all  water  was  drained  from 
the  boiler  and  the  contents  of  boiler  noted  for  each  1-inch  mark  of  the 
water-gauge,  with  the  following  results : 


Height  of  water 
in  gauge. 

Total 
water. 

Difference. 

Height  of  water 
in  gauge. 

Total 
water. 

Difference. 

Inches. 
0 
1 
2 
3 
4 

Pounds. 
9,312 
9,498 
9,662 
9,912 
10,137 

186 
164 
250 
225 

Inches. 
5 
6 

7 
8 

Pounds. 
10,368 
10,672 
10,943 
11,175 

231 
304 
271 
232 

Fires  were  started  in  the  boilers  with  light  wood  and  blower  in  use 
at  9.40  A.M.  Temperature  of  water  in  boiler,  72  degrees;  height  in 
glass,  1  inch. 

The  following  is  a  record  of  time  and  pressures  or  temperatures : 


Time  Elapsed. 

Steam  Pressure. 

Time  Elapsed. 

Steam  Pressure. 

Min. 
0 
5 
6 
8 
9 
10 

Sec. 
30 

Fires  started 
Steam  formed 
25  pounds 

45       " 
65       " 
85       " 

Min. 
11 
11 
11 
12 
12 

Sec. 

30 
55 
20 
40 

125  pounds 
155       " 
175       " 

195       " 
215 

An  examination  of  the  boiler  after  this  test  showed  no  injury  or 
change  in  its  condition  in  any  respect. 

Tests  of  a  Thorny  croft  Boiler. — Prof.  A.  B.  W.  Kennedy,  in  Proc. 
Inst.  C.  E.,  vol.  xcix.  p.  57,  1890,  reports  the  results  of  four  tests  of  a 
Thornycroft  boiler.  The  principal  figures  are  the  following: 


RESULTS  OF  STEAM-BOILER  TRIALS.  399 


Trial  No. 

1 

2 

3 

4 

Heating  surface,  sq.  ft  

1837 

1837         1 

.837 

1837 

26.2 

30 

30 

26.2 

Ratio  H.S.  to  G.S  

70.1 

61.2 

61.2 

70.1 

182 

171 

149 

180 

Temperature  of  air  ,  t  

69 

70 

60 

62 

Coal  per  sq.  ft.  of  grate  per  Lr.,  Ibs  

7.74 

18.60 

29.80 

66.80 

Water  per  sq,  ft.  of  H.S.  per  hr.,  Ibs  

1.24 

3.20 

4.70 

8.50 

Evaporation  from  and  at  212°  per  Ib.  of  coal.. 

421 
13.4 

540 
12.48 

610 
12.00 

777 
10.29 

86.8 

81.4 

78.2 

66.6 

Analyses  of  gases,  mean  : 

11.74 

— 

11.68 

12.60 

Carbon  monoxide,  CO  

0.10 

— 

0.62 

2.30 

Oxygen  

7.71 

— 

7.41 

4.45 

Nitrogen,  by  difference  

80.45 

— 

80.29 

80.65 

18.14 

(est.  17.8) 

17.4 

17.2 

Heat  balance  : 

Heat  absorbed  by  boiler  

86.8 

81.4 

78.2 

66.6 

"     lost  in  chimney-gases  

10.8 

15.0 

16.5 

20.3 

'  '     lost  by  formation  of  CO  

0.5) 

Q   ft 

J5.0 

9.2 

'  '     lost  by  radiation  and  unaccounted  for 

1.9  i 

12.3 

3.9 

100.0 

100.0 

100.0 

100.0 

Analysis  of  the  coal  : 

0.96 

Ash  

..     2.19 

Carbon  

..  87.76 

.  .     4.11 

..     4.98 

100.0 

Heating  value  of  the  coal  by  Prof.  Kennedy's  calculation  from 
the  analysis:  14,900  B.T.U.  per  Ib.;  by  direct  calorimetric  determina- 
tion, 15,450  B.  T.  U.  per  Ib. 

Comments  on  the  Thornycroft  and  the  Babcock  &  Wilcox  Tests. — 
By  the  use  of  formula  (16),  p.  220,  viz., 

=r 


'(K-tcf)S' 

the  value  of  a,  the  coefficient  of  performance,  has  been  calculated  for 
each  of  the  tests  of  the  Thornycroft  and  the  Babcock  &  Wilcox 
boilers,  of  which  the  records  are  given  above.  For  the  Thornycroft 
tests  A",  the  heating  value  of  the  coal  has  been  taken  at  15,200  per  Ib., 
as  the  value  per  pound  of  combustible  is  not  given  in  the  record,  and 
Ea  is  taken  as  the  evaporation  per  pound  of  coal.  R,  the  factor  for 
radiation,  is  taken  at  the  low  figure  of  0.05,  since  the  boiler  seems  to 
have  been  unusually  well  protected  from  loss  by  radiation ;  and  /,  the 
temperature  of  the  steam  above  the  atmospheric  temperature,  has 
been  taken  at  300°.  For  the  Babcock  &  Wilcox  tests  the  value  of  K 
is  taken  as  15,750,  the  average  heating  value  per  pound  of  combusti- 


400 


STEAM-BOILER  ECONOMY. 


ble  of  good  Pocahontas  coal.  The  value  of  t  is  taken  as  the  differ- 
ence between  the  temperature  of  the  steam  and  the  temperature  of 
the  air  entering  the  ash-pit.  It  ranges  from  289.9  in  test  No.  1  down 
to  132.1  in  test  No.  6H.  R  is  taken  at  0.1. 

The  values  of  a  thus  calculated,  together  with  other  data  of  the 
test,  for  reference,  are  given  below. 

THORNYCROFT  TESTS. 

Rate  of  driving,  W/8 =    1.24  3.2 

Evaporation,  Ea =  13.4  12.48 

Efficiency,  # 86.8  81.4 

Lbs.  dry  gas  per  Ib.  C.,  / =  21.24  [est.  21] 

Oxygen  in  the  gas,  % 7.71 

Calculated  value  of  a* 57  (?)  244 

BABCOCK  &  WILCOX  TESTS. 

Test  No.  1234567 

Rate  of  driving,  W/8 5.18  5.57  8.42  8.75  10.07      9.58     13.67 

Evaporation,^..... 12.19  12.70  11.47  11.50  11.43     11.12     10.52 

Efficiency,  $ 74.8  77.9  70.4  70.6  70.1    ,68.2      64.5 

Lbs.  dry  gas  per  Ib.  C.,/ 16.8  19.1  17.3  18.8  20.6      17.3       18.6 

Oxygen  in  the  gas,  % 4.5  5.7  4.2  5.7  6.9        4.8        5.8 

Calculated  value  of  a..             ..454  313  383  267  191        410        235 


4.7 
12.00 
78.2 
20.44 
7.41 
255 


8.5 
10.29> 
66.6 
16.89 

4.45 
403 


The  relation  of  the  efficiency  to  the  rate  of  driving,  in  both  sets 


84- 


« 

£80 
.78 


Tesfs. 


=« 


$3- 


imycrvi 


— O  D(WcooH&  Wilcox  >ests. 


3          4-56  7  8  9          10         II  \Z         K         V 

Lb&  of  Water  Evaporated  from  and  at  212°F.  per  sq.ft.  of  Heating  Surf,  per  Hour. 
FIG.  121.— THORNYCROFT  AND  BABCOCK  &  WILCOX  TESTS  COMPARED. 

of  tests,  is  plotted  in  the  diagram  Fig.  121.  There  are  also  plotted, 
for  comparison,  a  line  representing  the  maximum  theoretical  perform- 
ance of  a  boiler  in  .which  there  is  no  loss  by  radiation,  with  /,  or 
pounds  of  dry  gas  per  pound  of  carbon  =  20,  a  =  200,  t  —  300,  and 
7T—  15,750,  no  account  being  taken  of  the  loss  of  heat  due  to  super- 

*  The  value  of  a  obtained  from  the  first  test  is  so  low  as  to  indicate  an  error 
either  in  the  record  of  the  test  itself  or  in  the  assumptions  made  in  the  calculation. 
If  we  assume  no  loss  by  radiation,  making  R  =  0,  the  value  of  a  becomes  294. 
At  very  low  rates  of  driving  a  small  difference  in  the  assumed  value  of  R  makes 
a  great  difference  in  the  computed  value  of  a,  but  at  high  rates  of  driving  it  is  of 
small  importance. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


401 


heated  steam  in  the  chimney-gases ;  together  with  a  line  representing 
the  same  data  but  with  a  radiation  factor  of  R  =  0.1.  The  record 
of  the  seven  best  tests  made  at  the  Centennial  Exhibition,  taken  from 
the  diagram  Fig.  49,  p.  223,  is  also  shown. 

Comparing  the  results  of  the  tests  as  plotted  with  the  lines  of 
theoretical  maximum  performance,  it  will  be  seen  that  the  results  lie 
remarkably  close  to  the  lines.  The  two  tests  that  are  farthest  from 
the  line,  No.  1  of  the  Babcock  &  Wilcox  tests  and  No.  4  of  the 
Thornycroft  tests,  are  those  in  which  the  quantity  of  gas  per  pound 
of  carbon  are  the  least,  and  the  comparatively  low  results  in  these 
tests  are  therefore  no  doubt  due  to  imperfect  combustion. 

These  two  sets  of  tests,  taken  together,  form  the  best  record  of 
high  performance  at  widely  different  rates  of  driving  that  has  yet 
been  published.  The  record  is  above  that  of  the  best  records  obtained 
in  the  Centennial  tests  with  anthracite  coal. 

To  account  for  these  high  results  we  have  the  analyses  of  the 
chimney-gases,  which  show  that  in  the  best  tests  the  oxygen  in  the 
gas  is  over  5  per  cent  and  the  number  of  pounds  of  dry  gas  per  pound 
of  carbon  from  17  to  21.  The  best  results  correspond  to  low  values 
of  the  coefficient  of  performance,  a.  By  plotting  the  computed 


-4-5U 

400 
o50 
300 
250 

zo°, 

\ 

y 

U 

1 

\ 

\ 

32 

\ 

x 

x  Thorn 

ycrofr. 
W. 

07 

N 

^_ 

6         17        18         19         20   ~o  2 

fOU 

400 

j>  300 
E50 
2OO 

x 

V 

03 

\ 

\ 

J 

\ 

V 

X 

70 

Ss 

*-•  — 

—   — 

Lbs.of  Dry  Gas  per  lb.  Carbon. 

FIG.  122. — RELATION  OP  a  TO  LBS. 
OF  GAS  PER  LB.  C. 


'"A-  5  6          "07  ft 

Percent  Oxygen  in  Gases 
FIG.  123. — RELATION  OF  a  TO  OXYGEN 
IN  THE  GASES. 


values  of  a  with  reference  to  the  pounds  of  gas  per  pound  of  carbon, 
and  to  the  per  cent  of  oxygen  in  the  gas,  as  in  Figs.  122  and  123,  we 
find  that  the  minimum  value  of  a  seems  to  correspond  to  about 
21  Ibs.  of  gas  per  pound  of  carbon,  and  about  7  per  cent  oxygen  in 
the  gases.  The  rapid  rise  of  the  value  of  a  with  decrease  of  oxygen 
in  the  gases  is  to  be  expected,  because  the  value  calculated  by  the 


402  STEAM-BOILER  ECONOMY. 

formula  (16)  is  based  on  the  assumption  of  perfect  combustion,  and 
with  oxygen  less  than  7  per  cent  there  is  almost  always  some  carbonic 
oxide  present,  showing  that  the  combustion  is  imperfect.  When  the 
pounds  of  dry  gas  per  pound  of  carbon  exceed  21  and  the  per  cent 
of  oxygen  exceeds  8,  the  calculated  value  of  a  should  be  independent 
of  these  quantities. 

Since  high  efficiency,  according  to  formula  (15),  depends  on  both 
a  and  /  being  small,  and  since  a  is  aifected  by  /  so  as  to  increase 
rapidly  when  f  is  less  than  20,  it  is  evident  that  although  a  appears  to 
have  a  minimum  value  when  f  is  about  or  above  21,  maximum  effi- 
ciency will  be  obtained  when  a  is  at  some  value  higher  than  its  mini- 
mum value,  and  when  /  is  somewhat  less  than  21.  The  Babcock  & 
Wilcox  test  No.  7,  with  a  =  235  and/=  18.6,  gives  a  higher  relative 
efficiency  (as  compared  with  the  line  of  maximum  theoretical  perform- 
ance) than  test  No.  5.  with  a  =  191  andf=  20.6. 

The  record  of  the  Thornycroft  test  No.  1,  showing  86.8  per  cent 
efficiency,  probably  contains  some  error.  The  test  was  only  of  five 
hours'  duration,  and  only  1006  Ibs.  of  coal  was  burned  in  the  whole 
test.  A  slight  error  in  the  measurement  of  coal  or  water,  and 
especially  an  error  due  to  fluctuation  of  the  water-level,  would  make 
an  important  error  in  the  result  at  this  very  low  rate  of  driving. 

Tests  with  Anthracite  at  the  Centennial  Exhibition,  1876. — A 
brief  summary  of  these  tests  has  already  been  given  on  page  291,  and 
the  results  are  plotted  on  the  diagram,  Fig.  107,  page  290.  Some  of 
the  results  are  also  plotted  on  the  diagram,  Fig.  49,  page  223,  for  com- 
parison with  theoretical  performance  under  certain  assumed  condi- 
tions. Of  the  fourteen  boilers  tested,  illustrations  of  seven  have 
already  been  given,  as  follows:  Eoot,  page  268;  Firmenich,  page  265; 
Babcock  &  Wilcox,  page  266;  Galloway,  page  248;  Wiegand  and 
Kelly,  page  260;  Kogers  &  Black,  page  262.  The  Eoot  boiler  used  in 
the  test  differed  from  the  one  shown  on  page  268  in  not  having  the 
series  of  horizontal  longitudinal  steam-  and  water-drums,  a  single 
transverse  drum  being  used  instead.  The  other  seven  boilers  are 
illustrated  and  briefly  described  below. 

The  Lowe  boiler,  Fig.  124,  is  an  ordinary  cylindrical  tubular  boiler 
4  x  18^-  ft.  with  forty-six  tubes  3  ins.  X  15  ft.,  with  a  chamber  or 
connection  in  the  front  end  of  the  boiler,  the  rear  of  which  forms 
the  front  tube-sheet.  The  bridge-wall  back  of  the  grate  is  extended 
up  to  the  shell.  The  heated  gases  pass  through  side  openings  through 
the  water-space  into  the  front  chamber,  thence  through  the  tubes  to 
the  rear  of  the  boiler,  then  through  a  return-flue  along  the  lower  half 


RESULTS  OF  STEAM-BOILER  TRIALS. 


403 


of  the  shell  to  the  rear  of  the  bridge-wall,  when  they  rise  through 
two  side  flues,  and  circulating 
around  the  upper  half  of  the 
shell  and  a  superheating  drum, 
escape  to  the  uptake. 

The  Smith  boiler,  Fig.  125, 
is  an  ordinary  return-tubular 
boiler,  supplied  with  additional 
heating  surface  in  the  setting. 
From  the  hollow  cast  -  iron 
bridge-wall  a  number  of  pipes  FlG'  124— THE  LOWE  BOILER. 

run  horizontally  under  and  back  of  the  boiler  and  connect  to  short 
vertical  tubes  screwed  into  a  larger  horizontal  pipe  located  back  of  the 


FIG.  125. — THE  SMITH  BOILER. 

shell  and  connected  thereto.  In  addition  to  the  above,  two  cast-iron 
pipes  run  along  either  side  of  and  below  the  grate  and  are  connected 
with  the  water-space  in  the  shell.  In  the  latter  are  attached  on  either 
side  a  series  of  vertical  conical  castings,  bulb-shaped  at  their  tops,  with 


'oooo     oooo 

00000  00000 

ooooo  oooo 
ooooo  ooooo 
ooooo  ooooo 


FIG.  126. — THE  ANDREWS  BOILER. 

a  small  wrought-iron  pipe  in  each  as  an  outlet  for  steam,  and  the  several 
small  steam-pipes  are  connected  together  and  to  the  steam-space  of 
the  main  shell. 


404 


STEAM-BOILER  ECONOMY. 


The  Andrews  boiler,  Fig.  126,  is  of  the  double  marine  tubular  type 
with  internal  furnace  and  external  sheet-iron  connections  for  directing 
the  products  of  combustion  from  the  lower  set  of  tubes  to  the  upper. 
The  shell  is  rectangular  with  a  semi-cylindrical  top. 

The  Harrison  boiler,  Fig.  127.  consists  of  sections  of  hollow 
cast-iron  "spheres,  8  ins.  diameter,  with  curved  necks,  cast  in  groups 

of  two  and  four  and  held  together 
by  bolts  extending  through  the 
spheres  and  necks  the  entire  length 
of  the  sections.  The  sections  are 
set  side  by  side  at  the  angle  shown. 
The  Anderson  boiler,  Fig.  128, 
is  composed  of  sections,  each  con- 
taining nine  wrought-iron  tubes  3 
ins.  diameter  and  10  ft.  long,  which 
are  nearly  horizontal  and  arranged 
in  a  vertical  row.  The  four  lower 
tubes  are  secured  at  their  front  ends 
to  a  cast-iron  chamber  and  rise  a 
little  from  front  to  rear.  The  front 
ends  of  the  five  upper  tubes  are  similarly  attached  to  an  upper  cham- 
ber, and  slope  a  little  from  front  to  rear.  The  rear  ends  of  all  the 
tubes  are  united  by  a  manifold.  The  lower  front  chambers  are  con- 
nected at  their  lower  ends  and  the  upper  front  chambers  at  their  upper 


FIG.  127. — THE  HARRISON  BOILER. 


FIG.  128.— THE  ANDERSON  BOILER.  FIG.  129. — THE  EXETER  BOILER. 
ends.  A  horizontal  partition  is  placed  above  the  four  lower  tubes,  so 
as  to  compel  the  gases  to  flow  first  along  the  four  lower  tubes  and  then 
along  the  five  upper  tubes. 

The  Exeter  boiler,  Fig.  129,  consists  of  hollow,  rectangular,  cast- 
iron,  slab-shaped  sections  set  transversely,  with  twelve  oblong  openings 
in  two  horizontal  flues  through  each  section.  Twenty-seven  such 
sections  are  placed  one  in  the  rear  of  the  other  and  connected  through 
short  side  pipes  to  one  steam-  and  one  feed-pipe,  thus  forming  a  com- 
plete boiler.  Two  of  these  boilers  are  placed  side  by  side  over  one 
grate.  The  gases  from  the  grate  pass  to  the  rear  of  the  boiler  through 
the  lower  row  of  passages  and  return  through  the  upper  rows. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


405 


The  Pierce  boiler,  Fig.  130,  consists  of  a  flat-ended  cylinder 
directly  above  the  fire-grate,  revolving  on  trunnions.  The  heated 
gases  envelop  the  cylinder  and  enter  one  end  of  an  annular  row  of 
tubes  in  the  shell,  and  after  passing  through  them  return  through 
another  row  of  tubes  concentric  with  the  first  and  thence  escape  to  the 
chimney.  Cups  are  secured  around  the  tubes  of  the  outer  row,  to 


FIG.  130. — THE  PIERCE  BOILER. 

catch  the  water  whenever  the  tube  is  lifted  above  the  water-line  by  the 
revolving  of  the  shell,  and  thus  prevent  overheating  of  these  tubes  and 
of  the  shell.  The  feed-water  is  introduced  through  one  trunnion  and 
steam  is  taken  out  through  the  other. 

Some  of  the  conclusions  which  may  be  drawn  from  the  results  of 
the  Centennial  tests  are  the  following : 

1.  The  high  results  obtained  by  the  first  five  boilers  on  the  list, 
page  201,  viz.:  the  Eoot,  Firmenich,  Lowe,  Smith,  Babcock  &  TTilcox, 
and  Galloway  boilers,  constitute  a  standard  of  performance  which  has 
not  been  excelled  since  1876  in  any  properly  authenticated  series  of 
tests  with  anthracite  coal. 

2.  These  high  figures  being  obtained  with  boilers  of  widely  different 
types,  it  is  evident  that  economy  of  fuel  does  not  depend  to  any  great 
extent  on  the  type  of  boiler. 

3.  The  low  results  obtained  in  the  tests  of  all  the  other  boilers  are 
not  explained  by  their  design,  or  by  anything  in  the  record  of  their 
tests.     Of  the  possible  causes  of  low  performance  are  excessive  air- 
supply,  especially  at  the  higher  rates  of  driving ;  short-circuiting  of  the 
gases;    excessive   loss   by   radiation.      The   lack  of   analyses   of  the 
chimney-gases  prevents  the  drawing  of  any  definite  conclusions  in 
regard  to  the  air-supply. 


CHAPTER   XVI.* 


PROPERTIES   OF  WATER  AND  OF    STEAM— FACTORS    OF    EVAPORA- 
TION—CHIMNEYS. 

WATER. 

Weight  of  "Water  at  Different  Temperatures. — The  weight  of 
water  at  maximum  density,  39.1°,  is  generally  taken  at  the  figure 
given  by  Rankine,  62.425  Ibs.  per  cu.  ft.  Some  authorities  give  as  low 
as  62.379.  The  figure  62.5  commonly  given  is  approximate.  The 
highest  authoritative  figure  is  62.425.  At  62°  F.  the  figures  range 
from  62.291  to  62.360.  The  figure  62.355  is  generally  accepted  as  the 
most  accurate. 

At  32°  F.  figures  given  by  different  writers  range  from  62.379  to 
62.418.  Clark  gives  the  latter  figure  and  Hamilton  Smith,  Jr.  (from 
Rosetti),  gives  62.416. 

Weight  of  Water  at  Temperatures  above  212°  F. — Porter  (Rich- 
ards7 "  Steam-engine  Indicator/'  p.  52)  says  that  nothing  is  known 
about  the  expansion  of  water  above  212°.  Applying  formulae  derived 
from  experiments  made  at  temperatures  below  212°,  however,  the 
weight  and  volume  above  212°  may  be  calculated,  but  in  the  absence 
of  experimental  data  we  are  not  certain  that  the  formulas  hold  good 
at  higher  temperatures. 

Thurston,  in  his  "  Engine  and  Boiler  Trials,"  gives  a  table  from 
which  we  take  the  following  (neglecting  the  third  decimal  place  given 
by  him) : 


Ill 

gr 

212 
220 
230 
240 
250 
260 
270 

If 

Tempera- 
ture, 
deg.  F. 

H 

H 

,  a 
"M  '"  "o 

H 

II 
j|| 

S    fe 
£~ 

Iff 

59.71 
59.64 
59.37 
59.10 
58.81 
58.52 
58.21 

280 
290 
300 
310 
320 
330 
340 

57.90 
57.59 
57.26 
56.93 
56.58 
56.24 
55  '.88 

350 
860 
370 
380 
390 
400 
410 

55.52 
55.16 
54.79 
54.41 
51.03 
53.64 
53.26 

420 
430 
440 
450 
460 
470 
480 

52.86 
52.47 
52.07 
51.66 
51.26 
50.85 
50.44 

490 
500 
510 
520 
530 
540 
550 

50.03 
49.61 
49.20 
48.78 
48.36 
47.94 
47.52 

Box  on  Heat  gives  the  following : 

Temperature  F 212°       250°      300°      350° 

Lbs.  per  cubic  foot 59.8?.    58.85     57.42    55.94 


400'      450°      500° 
54.34    52.70    51.02 


600° 
47.64 


*This  chapter  is  compiled  from  the  author's  "Mechanical  Engineers'  Pocket- 
book." 

406 


PROPERTIES   OF    WATER. 


407 


At  212°  figures  given  by  different  writers  (see  Trans.  A.  S.  M.  E., 
xiii.  409)  range  fom  59.56  to  59.845,  averaging  about  59.77. 

Weight  of  Water  per  Cubic  Foot,  from  32°  to  212°  F.,  and  heav 
units  per  pound,  reckoned  above  32C  F.:  The  following  table,  made 
by  interpolating  the  table  given  by  Clark  as  calculated  from  Rankine's 


fi 

£ 

£ 

£ 

_3 

_o  •— 

DO 

3 

o  •« 

CO 

j3 

J§  *^ 

CO 

J.2 

to 

™r  3 

Si 

•a 

K- 

~  3 

Sfe 

r—  I  — 

g^ 

'"i's 

"a 

P.  ' 

•~  .  "o 

3 
• 

&« 

•S^P'S 

~ 

P.  • 

ifl^-g 

s 

5  • 

^U->-> 

J-s 

.£fo5  o 

1 

j! 

'55  p.fa 

cj 
0> 

w 

1" 

!** 

09 

W 

S  ^ 

ET 

'55  cLfe 

<& 

32 

62.42 

0. 

78 

62.25 

46.03 

123 

61.68 

91.16 

168 

60.81 

136.44 

33 

62.42 

1. 

79 

62.24 

47.03 

124 

61.67 

92.17 

169 

60.79 

137.45 

34 

62.42 

2. 

80 

6223 

48.04 

125 

61.65 

93.17 

170 

60.77 

138.45 

^5 

6242 

3. 

81 

62.22 

49.04 

126 

61.63 

94.17 

171 

60.75 

139.46 

36 

62.42 

4. 

82 

62.21 

50.04 

127 

61.61 

95.18 

172 

60.73 

140.47 

37 

62.42 

5. 

83 

62.20 

51.04 

128 

61.60 

96.18 

173 

60.70 

141.48 

38 

62.42 

6. 

84 

62.19 

52.04 

129 

61  58 

97.19 

174 

CO.  68 

142.49 

39 

62.42 

7. 

85 

62.18 

53.05 

130 

i  61.56 

98.19 

175 

60.66 

143.50 

40 

62.42 

8. 

86 

62.17 

54.05 

131 

61.54 

99.20 

176 

60.64 

144.51 

41 

62.42 

9. 

87 

62.16 

55.05 

132 

61.52 

100.20 

177 

60.62 

145.52 

42 

62.42 

10. 

88 

62.15 

56.05 

133 

61.51 

101.21 

178 

60.59 

146.52 

43 

62.42 

11. 

89 

62.14 

57.05 

134 

61.49 

102.21 

179 

60.57 

147.53 

44 

62.42 

12. 

90 

62.13 

58.06 

135 

61.47 

103.22 

180 

60.55 

148.54 

45 

62.42 

13. 

91 

62.12 

59.06 

136 

61.45 

104.22 

181 

60.53 

149.55 

46 

62.42 

14. 

92 

62.11 

60.06 

137 

61.43 

105.23 

182 

60.50 

150.56 

47 

62.42 

15. 

93 

62.10 

61.06 

188 

61.41 

106.23 

183 

00.48 

151.57 

48 

62.41 

16. 

94 

62.09 

62.06 

189 

61.39 

107.24 

184 

60.46 

152.58 

49 

62.41 

17. 

95 

62.08 

63.07 

140 

61.37 

108.25 

185 

60.44 

153.59 

50 

62.41 

18. 

96 

62.07 

64.07 

141 

61.36 

109.25 

186 

60.41 

154.60 

51 

62.41 

19. 

97 

62.06 

65.07 

142 

61.34 

110.26 

187 

60.39 

155.61 

52 

62.40 

20. 

98 

62.05 

66.07 

143 

61.32 

111.26 

188 

60.37 

156.62 

53 

62.40 

21.01 

99 

62.03 

67.08 

144 

61.30 

112.27 

189 

60.34 

157.63 

54 

62.40 

22.01 

100 

62.02 

68.08 

145 

61.28 

113.28 

190 

60.32 

158.64 

55 

62.39 

23.01 

101 

62.01 

69.08 

146 

61.26 

114.28 

191 

60.29 

159.65 

56 

62.39 

24.01 

102 

62.00 

70.09 

147 

61.24 

115.29 

192 

60.27 

160.67 

57 

62.39 

25.01 

103 

61.99 

71.09 

148 

61.22 

116.29 

193 

60.25 

161.68 

58 

62.38 

26.01 

104 

61.97 

72.09 

149 

61.20 

117.30 

194 

60.22 

162.69 

59 

62.38 

27.01 

105 

61.96 

73.10 

150 

61.18 

118.31 

195 

60.20 

163.70 

60 

62.37 

28.01 

106 

61.95 

74.10 

151 

61.16 

119.31 

196 

60.17 

164.71 

61 

62.37 

29.01 

107 

61.93 

75.10 

152 

61.14 

120.32 

197 

60.15 

165.73 

62 

62.36 

30.01 

108 

61.92 

76.10 

153 

61.12 

121.33 

198 

60.12 

166.73 

63 

62.36 

31.01 

109 

61.91 

77.11 

154 

61.10 

122.33 

199 

60.10 

167.74 

64 

62.35 

32.01 

110 

61.89 

78.11 

155 

61.08 

123.34 

200 

60.07 

168.75 

65 

62.34 

33.01 

111 

61.88 

79.11 

156 

61-06 

124.35 

201 

60.05 

169.77 

66 

62.34 

34.02 

112 

61.86 

80.12 

157 

61.04 

125.35 

202 

60.02 

170.78 

67 

62.33 

35.02 

113 

61.85 

81.12 

158 

61.02 

126.36 

203 

60.00 

171.79 

68 

62.33 

36.02 

114 

61.83 

8213 

159 

,61.00 

127.37 

204 

59.97 

172.80 

69 

62.32 

37.02 

115 

61.82 

83.13 

160 

.60.98 

128  37 

205 

59.95 

173.81 

70 

62.31 

38.02 

116 

61.80 

84.13 

161 

60.96 

129.38 

206 

59.92 

174.83 

71 

62.31 

39.02 

117 

61.78 

85.14 

162 

60.94 

130.39 

207 

59.89 

175.84 

72 

62.30 

40.02 

118 

61.77 

86.14 

163 

60.92 

131.40 

208 

59.87 

176.85 

73 

62.29 

41.02 

119 

61.75 

87.15 

164 

60.90 

132.41 

209 

59.84 

177.86 

74 

62.28 

42.03 

120 

61.74 

88.15 

165 

60.87 

133.41 

210 

59.82 

178.87 

75 

62.28 

43.03 

121 

61.72 

89.15 

166 

60.85 

134.42 

211 

59.79 

179.89 

76 

62.27 

44.03 

122 

61.70 

90.16 

167 

60.83 

135.43 

212 

59.76 

180.90 

77 

62.26 

4503 

4:08  STEAM-BOILER  ECONOMY. 

formula,  with  corrections  for  apparent  errors,  was  published  by  the 
author  in  1884,  Trans.  A.  S.  M.  E.,  vi.  90.  (For  heat-units  above 
212°  see  Steam  Tables.) 

STEAM. 

The  Temperature  of  Steam  in  contact  with  water  depends  upon 
the  pressure  under  which  it  is  generated.  At  the  ordinary  atmos- 
pheric pressure  (14.7  Ibs.  per  sq.  in.)  its  temperature  is  212°  F.  As 
the  pressure  is  increased,  as  by  the  steam  being  generated  in  a  closed 
vessel,  its  temperature,  and  that  of  the  water  in  its  presence,  increases. 

Saturated  Steam  is  steam  of  the  temperature  due  to  its  pressure 
— not  superheated. 

Superheated  Steam  is  steam  heated  to  a  temperature  above  that 
due  to  its  pressure. 

Dry  Steam  is  steam  which  contains  no  moisture.  It  may  be  either  • 
saturated  or  superheated. 

Wet  Steam  is  steam  containing  intermingled  moisture,  mist,  or 
spray.  It  has  the  same  temperature  as  dry  saturated  steam  of  the 
same  pressure. 

Water  introduced  into  the  presence  of  superheated  steam  will  flash 
into  vapor  until  the  temperature  of  the  steam  is  reduced  to  that  due 
its  pressure.  Water  in  the  presence  of  saturated  steam  has  the  same 
temperature  tu?  the  steam.  Should  cold  water  be  introduced,  lowering 
the  temperature  of  the  whole  mass,  some  of  the  steam  will  be  con- 
densed, reducing  the  pressure  and  temperature  of  the  remainder, 
until  an  equilibrium  is  established. 

Temperature  and  Pressure  of  Saturated  Steam. — The  relation 
between  the  temperature  and  the  pressure  of  steam,  according  to 
Regnault's  experiments,  is  expressed  by  the  formula  (Buchanan's,  as 

2938  16 
given  by  Clark)  t  =  6.1998644'_  logl>  -  371.85,  in  which  p  is  the 

pressure  in  pounds  per  square  inch  and  t  the  temperature  of  the 
steam  in  Fahrenheit  degrees.  It  applies  with  accuracy  between 
120°  F.  and  446°  F.,  corresponding  to  pressures  of  from  1.68  Ibs.  to 
445  Ibs.  per  sq.  in.  (For  other  formulae  see  Wood's  and  Peabody's 
"  Thermodynamics/') 

Latent  Heat  of  Steam. — The  formula  for  latent  heat  of  steam, 
as  given  by  Raiikine  and  others,  is  L  =  1091.7  —  .695(tf  —  32°). 

Total  Heat  of  Saturated  Steam  (above  32°  F.). — According  to 
Eegnault's  experiments,  the  formula  for  total  heat  of  steam  is 
H=  1091.7  +  .305(zf-  32°),  in  which  t  is  temperature  Fahr.  and 
H  the  heat-units.  (Rankine) 

The  total  heat  in  steam  (above  32°)  includes  three  elements: 

1st.  The  heat  required  to  raise  the  temperature  of  the  water  to 
the  temperature  of  the  steam. 

2d.  The  heat  required  to  evaporate  the  water  at  that  temperature, 
called  internal  latent  heat. 


PROPERTIES   OF  STEAM.  409 

3d.  The  latent  heat  of  volume,  or  the  external  work  done  by  the 
steam  in  making  room  for  itself  against  the  pressure  of  the  super- 
incumbent atmosphere,  (or  surrounding  steam  if  inclosed  in  a  vessel). 

The  sum  of  the  last  two  elements  is  called  the  latent  heat  of 
steam.  In  Buel's  tables  (Weisbach,  vol.  ii,  Dubois's  translation)  the 
two  elements  are  given  separately. 

Density  and  Volume  of  Saturated  Steam,  —  The  density  of  steam  is 
expressed  by  the  weight  of  a  given  volume,  say  1  cu.  ft.;  and  the 
volume  is  expressed  by  the  number  of  cubic  feet  in  one  Ib.  of  steam. 

Mr.  Brownlee's  expression  for  the  density  of  saturated  steam  iiv 

00.941 

terms  of  the  pressure  is  D  =    ^        ,  or  log  D  •—  0.941/j  —  2.519,  in 

ooO.ob 

which  D  is  the  density,  and  p  the  pressure  in  pounds  per  square  inch. 
In  this  expression,  jK°'941  is  the  equivalent  of  p  raised  to  the  16/17 
power,  as  employed  by  Rankine. 

The  volume  v  being  the  reciprocal  of  the  density, 

v=??^,    or   log  v  =  2.519  -0.941  log  p. 

Relative  Volume  of  Steam.  —  The  relative  volume  of  saturated 
steam  is  expressed  by  the  number  of  volumes  of  steam  produced  from 
one  volume  of  water  at  39°  F.  The  relative  volume  is  found  by  mul- 
tiplying the  volume  in  cu.  ft.  of  one  Ib.  of  steam  by  the  weight  of  a 
cu.  ft.  of  water  at  39°  F.,  or  62,425  Ibs. 

Gaseous  Steam,  —  When  saturated  steam  is  superheated,  or  sur- 
charged with  heat,  it  advances  from  the  condition  of  saturation  into 
that  of  gaseity.  The  gaseous  state  is  only  arrived  at  by  considerably 
elevating  the  temperature,  if  the  pressure  remains  the  same.  Steam 
thus  sufficiently  superheated  is  known  as  gaseous  steam  or  steam-gas. 

The  Specific  Heat  of  Gaseous  Steam  is  0.475,  under  constant  pres- 
sure, as  found  by  Eegnault.  It  is  identical  with  the  coefficient  of 
increase  of  total  heat  for  each  degree  of  temperature.  [This  is  at 
atmospheric  pressure  and  212°  F.  He  found  it  not  true  for  any  other" 
pressure.  Theory  indicates  that  it  would  be  greater  at  higher  tem- 
peratures. (Prof.  Wood.)] 

Total  Heat  of  Gaseous  Steam.  —  Wood  gives  for  the  total  heat 
(above  32°)  of  superheated  steam  H=  1091.7  +  0.48(*  -  32°). 

The  Specific  Density  of  Gaseous  Steam  is  0.622,  that  of  air  being  1. 
That  is  to  say,  the  weight  of  a  cubic  foot  of  gaseous  steam  is  about 
five-eighths  of  that  of  a  cubic  foot  of  air  of  the  same  pressure  and 
temperature. 

The  density  or  weight  of  a  cubic  foot  of  gaseous  steam  is  expressi- 
ble by  the  formula 

_2,7074pxO.G22_ 

"""       ~ 


461' 

in  which  D'  is  the  weight  of  a  cubic  foot  of  gaseous  steam,  p  the  total 
pressure  in  Ibs.  per  square  inch,  and  t  the  temperature  Fahrenheit. 


410 


STEAM-BOILER  ECONOMY. 


Identification  of  Dry  Steam  by  Appearance  of  a  Jet. — Prof. 
Denton.  (Trans.  A.  S.  M.  E.,  vol.  x)  found  that  jets  of  steam  show 
unmistakable  change  of  appearance  to  the  eye  when  steam  varies  less 
than  1  per  cent  from  the  condition  of  saturation  either  in  the  direc- 
tion of  wetness  or  superheating. 

If  a  jet  of  steam  flow  from  a  boiler  into  the  atmosphere  under 
circumstances  such  that  very  little  loss  of  heat  occurs  through  radia- 
tion, etc.,  and  the  jet  be  transparent  close  to  the  orifice,  or  be  even  a 
grayish-white  color,  the  steam  may  be  assumed  to  be  so  nearly  dry 
that  no  portable  condensing  calorimeter  will  be  capable  of  measuring 
the  amount  of  water  in  the  steam.  If  the  jet  be  strongly  white,  the 
amount  of  water  may  be  roughly  judged  up  to  about  2  per  cent,  but 
beyond  this  a  calorimeter  only  can  determine  the  exact  amount  of 
moisture. 

Table  of  the  Properties  of  Saturated  Steam. — In  the  table  of 
properties  of  saturated  steam  on  the  following  pages  the  figures  for 
temperature,  total  heat,  and  latent  heat  are  taken,  up  to  210  Ibs. 
absolute  pressure,  from  the  tables  in  Porter's  "  Steam-engine  Indi- 
cator." The  figures  for  weight  per  cubic  foot  and  for  cubic  feet  per 
pound  have  been  taken  from  Dwelshauvers-Dery's  table,  Trans.  A.  S. 
M.  E.,  vol.  xi.  The  figures  for  relative  volume  are  from  BueFs  table, 
in  Dubois's  translation  of  Weisbach,  vol.  ii.  From  211  to  219  Ibs.  the 
figures  for  temperature,  total  heat,  and  latent  heat  are  from  Dwels- 
hauvers's  table;  and  from  220  to  1000  Ibs.  all  the  figures  are  from 
Buel's  table. 


WEIGHT   OF   1    CUBIC   FOOT   OF    STEAM    IN    DECIMALS   OF   A   POUND. 
OF    DIFFERENT   AUTHORITIES. 


COMPARISON 


Absolute 
Pressure, 
Ibs.  per  sq.  in. 

Weight  of  1  Cubic  Foot  according  to 

Absolute 
Pressure, 
Ibs.  per  sq.  in 

Weight  of  1  Cubic  Foot  according  to 

Porter. 

Clark. 

Buel. 

Dwels- 
hauvers 

Pea- 
body. 

Porter. 

Clark. 

Buel. 

Dwels- 
hauvers 

Pea- 
body. 

1 
14.7 
20 
40 
60 
80 
100 

.0030 
.03797 
.0511 
.0994 
.  1457 
.19015 
.23302 

.003 
.0380 
.0507 
.0974 
.1425 
.1869 
.2307 

.00303 
.03793 
.0507 
.0972 
.1424 
.1866 
.2303 

.00299 

.00299 
.0376 
.0502 
.0964 
.1409 
.1843 
.2271 

120 
140 
160 
180 
200 
220 
240 

.27428 

.31386 
.35209 
.38895 
.42496 

.2738 
.3162 
.3590 
.4009 
.4431 
.4842 
.5248 

.2735 
.3163 
.3589 
.4012 
.4433 
.4852 
.5270 

.2724 
.3147 
.3567 
.3983 
.4400 

.2695 
.3113 
.3530 
.3945 
.4359 
.4772 
.5186 

.0507 
.0972 
.1422 
.1862 
.2296 

There  are  considerable  differences  between  the  figures  of  weight 
and  volume  of  steam  as  given  by  different  authorities.  Porter/s 
figures  are  based  on  the  experiments  of  Fairbairn  and  Tate.  The 
figures  given  by  the  other  authorities  are  derived  from  theoretical 
formulae  which  are  believed  to  give  more  reliable  results  than  the 
experiments.  The  figures  for  temperature,  total  heat,  and  latent  heat 
as  given  by  different  authorities  show  a  practical  agreement,  all  being 
derived  from  Kegnault's  experiments.  See  Peabody's  Tables  of 
Saturated  Steam;  also  Jacobus,  Trans.  A.  S.  M.  E.,  vol.  xii.  593. 


PROPERTIES   OF  STEAM. 


411 


PROPERTIES  OF  SATURATED  STEAM. 


€a 

Total  Heat  above 

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1091.7 

1091.7 

208080 

3338.3 

.00030 

29.67 

.122 

40 

8 

1094.1 

1086.1 

154330 

2472.2 

.00040 

29  56 

.176 

50 

18 

1097.2 

1079.2 

107630 

1724.1 

.00058 

29.40 

.254 

60 

28.01 

1100.2 

1072.2 

76370 

1223.4 

.00082 

29.19 

.359 

70 

38.02 

1103.3 

1065.3 

54660 

875.61 

.00115 

28.90 

.502 

80 

48.04 

1106.3 

1058.3 

39690 

635.80 

.00158 

28.51 

.692 

90 

58.06 

1109.4 

1051.3 

29290 

469.20 

.00213 

28.00 

.943 

100 

68.08 

1112.4 

1044.4 

21830 

349.70 

.00280 

27.88 

1 

102.1 

70.09 

1113.1 

1043.0 

20623 

334.23 

.00299 

25.85 

2 

126.3 

94.44 

1120.5 

1026.0 

10730 

173.23 

.00577 

23.83 

3 

141.6 

109.9 

1125.1 

1015.3 

7325 

117.98 

.00848 

21.78 

4 

153.1 

121  4 

1128.6 

1007.2 

5588 

89.80 

.01112 

19.74 

5 

162.3     130.7 

1131.4 

1000.7 

4530 

72.50 

.01373 

17.70 

6 

170.1 

138.6 

1133.8 

995.2 

3816 

61.10 

.01631 

15.67 

7 

176.9 

145.4 

1135.9 

990.5 

3302 

53.00 

.01887 

13.63 

8 

182.9 

151.5 

1137.7 

986.2 

2912 

46.60 

.02140 

11.60 

9 

188.3 

156.9 

1139.4 

982.4 

2607 

41.82 

.02391 

9.56 

10 

193.2 

161.9 

1140.9 

979.0 

2361 

37.80 

.02641 

7.52 

11 

197.8 

166.5 

1142.3 

975.8 

2159 

34.61 

.02889 

5.49 

12 

202.0 

170.7 

1143.5 

672.8 

1990 

31.90 

.03136 

3.45 

13 

205.9 

174.7 

1144.7 

970.0 

1846 

29.58 

.03381 

1.41 

14 

209.6 

178.4 

1145.9 

967.4 

1721 

27.59 

.03625 

Gauge- 

pressure 
Ibs.  per 
sq.  in. 

14.7 

212 

180.9 

1146.6 

965.7 

1646 

26.36 

.03794 

0.304 

15 

213.0 

181.9 

1146  9 

065.0 

1614 

25.87 

.03868 

1.3 

16 

216.3 

185.3 

1147.9 

962.7 

1519 

24.33 

.04110 

2.3 

17 

219.4 

188.4 

1148.9 

960.5 

1434 

22.98 

.04352 

3.3 

18 

222.4 

191.4 

1149.8 

958.3 

1359 

21.78 

.04592 

4.3 

19 

225.2 

194.3 

1150.6 

956.3 

1292 

20.70 

.04831 

5.3 

20 

227.9 

197.0 

1151.5 

954.4 

1231 

.    19.72 

.05070 

6.3 

21 

230.5 

199.7 

1152.2 

952.6 

1176 

18.84 

.05308 

7.3 

22 

233.0 

202.2 

1153.0 

950.8 

1126 

18.03 

.05545 

8.3 

23 

235.4 

204.7 

.7 

949.1 

1080 

17.30 

.05782 

9.3 

24 

237.8 

207.0 

1154.5 

947.4 

1038 

16.62 

.06018 

10.3 

25 

240.0 

209.3 

1155.1 

945.8 

998.4 

15.99 

.06253 

11.3 

26 

242.2 

211.5 

.8 

944.3 

962.3 

15.42 

.06487 

12.3 

27 

244.3 

213.7 

1156.4 

942.8 

928.8 

14.88 

.06721 

13.3 

28 

246.3 

215.7 

1157.1 

941.3 

897.6 

14.38 

.06955 

14.3 

29 

248.3 

217.8 

.7 

939.9 

868.5 

13.91 

.07188 

15.3 

30 

250.2 

219.7 

1158.3 

938.9 

841.3 

13.48 

.07420 

16.3 

31 

252.1 

221.6 

.8 

937.2 

815.8 

13.07 

.07652 

17.8 

32 

254.0 

223.5 

1159.4 

935.9 

791.8 

12.63 

.07884 

18.3 

33 

255.7 

225.3 

.9 

934.6 

769.2 

12.32 

.08115 

19.3 

34 

257.5 

227.1 

1160.5 

933.4 

748.0 

11.98 

.08346 

20.3 

35 

259.2 

228.8 

1161.0 

932.2 

727.9 

11.66 

.08576 

21.3 

36 

260.8 

230.5 

.5 

931.0 

708.8 

11.36 

.08806 

22.3 

37 

262.5 

232.1 

1162.0 

929.8 

690.8 

11.07 

.09035 

STEAM-BOILER  ECONOMY. 


PROPERTIES   OF   SATURATED   STEAM.— Continued. 


£5 
g* 

gM 

I* 

tow 

%2 
o 

3  y 

lit 
II 

j! 

< 

If 
B- 

|2 

Total  Heat  above 
3.°F. 

Latent  Heat  L. 

TJ  k 
—  Ji  —  fl*. 

Heat-units. 

Relative  Volume, 
Volume  of  Water 
at  39°  F.  =  1. 

Volume.  Cu.  ft. 
in  1  Ib.  of  Steam. 

Weight  of  1  Cubic 
Foot  of  Steam. 
Pounds. 

In  the 
Water. 
k 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

23.3 

38 

264.0 

233.8 

1162.5 

928.7 

673.7 

10.79 

.09264 

24.3 

39 

265.6 

235.4 

.9 

927.6 

657.5 

10.53 

.09493 

25.3 

40 

267.1 

236.9 

1163.4 

926.5 

642.0 

10.28 

.09721 

26.3 

41 

268.6 

238.5 

.9 

925.4 

627.3 

10.05 

.09949 

27.3 

42 

270.1 

240.0 

1164.3 

924.4 

613.3 

9.83 

.1018 

28.3 

43 

271.5 

241.4 

.7 

923.3 

599.9 

9.61 

.1040 

29.3 

44 

272.9 

242,9 

1165.2 

922.3 

587.0 

941 

.1063 

30.3 

45 

274.3 

244.3 

.6 

921.3 

574.7 

9.21 

.1086 

31.3 

46 

275.7 

245.7 

1166.0 

920.4 

563.0 

9.02 

.1108 

32.3 

47 

277.0 

247.0 

.4 

919.4 

551.7 

8.84 

.1131 

33.3 

48 

278.3 

248.4 

.8 

918.5 

540.9 

8.67 

.1153 

34.3 

49 

279.6 

249.7 

1167.2 

917.5 

530.5 

8.50 

.1176 

35.3 

50 

280.9 

251.0 

.6 

916.6 

520.5 

8.34 

.1198 

36.3 

51 

282.1 

252.2 

1168.0 

915.7 

510.9 

8.19 

.1221 

37.3 

52 

283.3 

253.5 

.4 

914.9 

501.7 

8.04 

.1243 

38.3 

53 

284.5 

254.7 

.7 

914.0 

492.8 

7.90 

.1266 

39.3 

54 

285.7 

256.0 

1169.1 

913.1 

484.2 

7.76 

.1288 

40.3 

55 

286.9 

257.2 

.4 

912.3 

475.9 

7.63 

.1311 

41.3 

56 

288.1 

258.3 

.8 

911.5 

467.9 

7.50 

.1333 

42.3 

57 

289.1 

259.5 

1170.1 

910.6 

460.2 

7.38 

.1355 

43.3 

58 

290.3 

260.7 

.5 

909.8 

452.7 

7.26 

.1377 

44.3 

59 

291.4 

261.8 

.8 

909.0 

445.5 

7.14 

.1400 

45.3 

60 

292.5 

262.9 

1171.2 

908.2 

438.5 

7.03 

.1422 

46.3 

61 

293.6 

264.0 

.5 

907.5 

431.7 

6.92 

.1444 

47.3 

62 

294.7 

265.1 

.8 

906.7 

425.2 

6.82 

.1466 

48.3 

63 

295.7 

266.2 

1172.1 

905.9 

418.8 

6.72 

.1488 

49.3 

64 

296.8 

267.2 

.4 

905.2 

412.6 

6.62 

.1511 

50.3 

65 

297.8 

268.3 

.8 

904.5 

406.6 

6.53 

.1533 

51.3 

66 

298.8 

269.3 

1173.1 

903.7 

400.8 

6.43 

.1555 

52.3 

67 

299.8 

270.4 

.4 

903.0 

395.2 

6.34 

.1577 

53.3 

68 

300.8 

271.4 

.7 

902.3 

389.8 

6.25 

.1599 

54.3 

69 

301.8 

272.4 

1174.0 

901.6 

384.5 

6.17 

.1621 

55.3 

70 

302.7 

273.4 

.3 

900.9 

379.3 

6.09 

.1643 

56.3 

71 

303.7 

274.4 

.6 

900.2 

374.3 

601 

.1665 

57.3 

72 

304.6 

275.3 

.8 

899.5 

369.4 

5.93 

.1687 

58.3 

73 

305.6 

276.3 

1175.1 

898.9 

364.6 

5.85 

.1709 

59.3 

74 

306.5 

277.2 

.4 

898.2 

360.0 

5.78 

.1731 

60.3 

75 

307.4 

278.2 

.7 

897.5 

355.5 

5.71 

.1753 

61.3 

76 

308.3 

279.1 

1176.0 

896.9 

351.1 

5.63 

.1775 

62.3 

77 

309.2 

280.0 

.2 

896.2 

346.8 

5.57 

.1797 

63.3 

78 

310.1 

280.9 

.5 

895.6 

342.6 

5.50 

.1819 

64.3 

79 

310.9 

281.8 

.8 

895.0 

338.5 

5.43 

.1840 

65.3 

80 

311.8 

282.7 

1177.0 

894.3 

334.5 

5.37 

.1862 

66.3 

81 

312.7 

283.6 

.3 

893.7 

330.6 

5.31 

.1884 

67.3 

82 

313.5 

284.5 

.6 

893.1 

326.8 

525 

.1906 

68.3 

83 

314.4 

285.3 

.8 

892.5 

323.1 

5.18 

.1928 

69.3 

84 

315.2 

286.2 

1178.1 

891.9 

319.5 

5.13 

.1950 

70.3 

85 

316.0 

287.0 

.3 

891.3 

315.9 

5.07 

.1971 

PROPERTIES   OF  STEAM. 


PROPERTIES  OF   SATURATED   STEAM.— Continued. 


Gauge-pressure, 
Ibs.  per  sq.  in. 

Absolute  Press- 
ure, Ibs.  pei- 
Square  Inch. 

Temperature, 
Fahrenheit. 

Total  Heat  above 
32°  F. 

Latent  Heat  L. 
=  H  -  h. 
Heat-units. 

Relative  Volume. 
Vol.  of  Water 
at39°F.  =  1. 

.2*0 

p 

i>-=  g 

11! 

"ofeCQ 
> 

Weight  of  1  Cu. 
Foot  of  Steam. 
Pounds. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

71.3 

86 

316.8 

287.9 

1178.6 

890.7 

312.5 

5.02 

.1993 

72.3 

87 

317.7 

288.7 

.8 

890.1 

309.1 

4.96 

.2015 

73.3 

88 

318.5 

289.5 

1179.1 

889  5 

305.8 

4.91 

.2036 

74.3 

89 

319.3 

290.4 

.3 

888.9 

302.5 

4.86 

.2058 

75.3 

90 

320.0 

291.2 

.6 

888.4 

299.4 

4.81 

.2080 

76.3 

91 

320.8 

292.0 

.8 

887.8 

296.3 

4.76 

.2102 

77.3 

92 

321.6 

292.8 

1180.0 

887.2 

293.2 

4.71 

.2123 

78.3 

93 

322.4 

293.6 

.3 

886.7 

290.2 

4.66 

.2145 

79.3 

94 

323.1 

294.4 

.5 

886.1 

'287.3 

4.62 

.2166 

80.3 

95 

323.9 

295.1 

.7 

885.6 

284.5 

4.57 

.2188 

81.3 

96 

324.6 

295.9 

1181.0 

"885.0 

281.7 

4.53 

.2210 

82.3 

97 

325.4 

296.7 

.2 

884.5 

279.0 

4.48 

.2231 

83.3 

98 

326.1 

297.4 

.4 

884.0 

276.3 

4.44 

.2253 

84.3 

99 

326.8 

298.2 

.6 

883.4 

273.7 

4.40 

.2274 

85.3 

100 

327.6 

298.9 

.8 

882.9 

271.1 

4.36 

.2296 

86.3 

101 

328.3 

299.7 

1182.1 

882.4 

268.5 

4.32 

.2317 

87.3 

102 

329.0 

300.4 

.3 

881.9 

266.0 

4.28 

.2339 

88.3 

103 

329.7 

301.1 

.5 

881.4 

263.6 

4.24 

.2360 

89.3 

104 

330.4 

301.9 

.7 

880.8 

261.2 

4.20 

.2382 

90.3 

105 

331.1 

302.6 

.9 

880.3 

258.9    4.16 

.2403 

91.3 

106 

331.8 

303.3 

1183.1 

879.8 

2566    4.12 

.2425 

92.3 

107 

332.5 

3040 

.4 

879.3 

254.3 

4.09 

.2446 

93.3 

108 

333.2 

3047 

.6 

878.8 

252.1 

4.05 

.2467 

94.3 

109 

333.9 

305.4 

.8 

878.3 

249.9 

4.02 

.2489 

95.3 

110 

334.5 

306.1 

1184.0 

877.9 

247.8 

3.98 

.2510 

96.3 

111 

335.2 

306.8 

.2 

877.4 

245.7 

3.95 

.2531 

97.3 

112 

335.9 

307.5 

.4 

876.9 

243.6 

3.92 

.2553 

98.3 

113 

336.5 

308.2 

.6 

876.4 

241.6 

3.88 

.2574 

99.3 

114 

337.2 

308.8 

.8 

875.9 

239.6 

3.85 

.2596 

100.3 

115 

3378 

309.5 

1185.0 

875.5 

237.6 

3.82 

.2617 

101.3 

116 

338.5 

310.2 

.2 

875.0 

235.7 

3.79 

.2638 

102.3 

117 

339.1 

310.8 

.4 

874.5 

233.8 

3.76 

.2660 

103.3 

118 

339.7 

311.5 

.6 

874.1 

231.9 

3.73 

.2681 

104.3 

119 

340.4 

312.1 

.8 

873.6 

230.1 

370 

.2703 

1053 

120 

341.0 

312.8 

.9 

873.2 

228.3 

3.67 

.2724 

106.3 

121 

341.6 

313.4 

1186.1 

872.7 

226.5 

3.64 

.2745 

107.3 

122 

3422 

314.1 

.3 

872.3 

224.7 

3.62 

.2766 

108.3 

123 

342.9 

314.7 

.5 

871.8 

223.0 

3.59 

.2788 

109.3 

124 

343.5 

315.3 

.7 

871.4 

221.3 

3.56 

.2809 

110.3 

125 

344.1 

316.0 

.9 

S70.9 

219.6 

3.53 

.2830 

111.3 

126 

344  7 

316.6 

1187.1 

870.5 

218.0 

3.51 

.2851 

112.3 

127 

.345.3 

317.2 

.3 

870.0 

2164 

3.48 

.2872 

113.3 

128 

345.9 

317.8 

.4 

869.6 

214.8 

3.46 

.2894 

114.3 

129 

346.5 

318.4 

.6 

869.2 

213.2 

3.43 

.2915 

115.3 

130 

347.1 

319  1 

.8 

868.7 

211.6 

3.41 

.2936 

116.3 

131 

347.6 

319.7 

1188.0 

868.3 

210.1 

3.38 

.2957 

117.3 

132 

348.2 

320.3 

.2 

867.9 

208.6 

336 

.2978 

118  3 

133 

348.8 

320.8 

.3 

867.5 

207.1 

3.33 

.3000 

119.3 

134 

349.4 

321.5 

.5 

867.0 

205.7 

331 

.3021 

414 


STEAM-BOILER  ECONOMY. 


PROPERTIES  OF   SATURATED   STEAM.— Continued. 


of  C 

I* 

rt 

II 

Absolute  Pres- 
sure, Ibs.  per 
Square  Inch. 

•TjJ 

ii 

1! 
t 

Total  Heat 
above  32°  F. 

Latent  Heat  L. 
=  H-h. 
Heat-units. 

Relative  Volume. 
Vol.  of  Water 
at39°F.  =  1. 

Volume.  Cubic 
IFeet  in  1  Ib. 
of  Steam. 

Weight  of  1  Cu. 
Foot  Steam, 
Pounds. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

120.3 

135 

350.0 

322.1 

1188.7 

866.6 

204.2 

3.29 

.3042 

121.3 

136 

350.5 

322.6 

.9 

866.2 

202.8 

3.27 

.3063 

122.3 

137 

351.1 

323.2 

1189.0 

865.8 

201.4 

3.24 

.3084 

123.3 

138 

351.8 

323.8 

.2 

865.4 

200.0 

3.22 

.3105 

124.3 

139 

352.2 

324.4 

.4 

865.0 

198.7 

3.20 

.3126 

125.3 

140 

352.8 

325.0 

.5 

864.6 

197.3 

3.18 

.3147 

126.3 

141 

353.3 

325.5 

.7 

864.2 

196.0 

3.16 

.3169 

1273 

142 

353.9 

326.1 

.9 

863.8 

194.7 

3.14 

.3190 

128.3 

143 

354,4 

326.7 

1190.0 

863.4 

193.4 

3.11 

.3211 

129.3 

144 

355.0 

327.2 

.2 

863.0 

192.2 

3.09 

.3232 

130.3 

145 

355.5 

327.8 

.4 

862.6 

190.9 

3.07 

.3253 

131.3 

146 

356.0 

328.4 

.5 

862.2 

189.7 

3.05 

.3274 

132.3 

147 

356.6 

328.9 

.7 

861.8 

188.5 

3.04 

.3295 

133.3 

148 

357.1 

329.5 

.9 

861.4 

187.3 

3.02 

.3316 

134.3 

149 

357.6 

330.0 

1191.0 

861.0 

186.1 

3.00 

.3337 

135.3 

150 

358.2 

330.6 

.2 

860.6 

184.9 

2.98 

.3358 

136.3 

151 

358.7 

331.1 

.3 

860.2 

183.7 

2.96 

.3379 

137.3 

152 

359.2 

331.6 

.5 

859.9 

182.6 

2.94 

.3400 

138.3 

153 

359.7 

332.2 

.7 

859.5 

181.5 

2.92 

.3421 

139.3 

154 

360.2 

332.7 

.8 

859.1 

180.4 

2.91 

.3442 

140.3 

155 

360.7 

333.2 

1192.0 

858.7 

179.2 

2.89 

.3463 

141.3 

156 

361.3 

333.8 

.1 

858.4 

178.1 

2.87 

.3483 

142.3 

157 

361.8 

334.3 

.3 

858.0 

177.0 

2.85 

.3504 

143.3 

158 

362.3 

334.8 

.4 

857.6 

176.0 

2.84 

.3525 

144.3 

159 

362.8 

335.3 

.6 

857.2 

174.9 

2.82 

.3546 

145.3 

160 

363.3 

335.9 

.7 

856.9 

173.9 

2.80 

.3567 

146.3 

161 

363.8 

336.4 

.9 

856.5 

172.9 

2.79 

.3588 

147.3 

162 

364.3 

336.9 

1193.0 

856.1 

171.9 

2.77 

.3609 

148.3 

163 

364.8 

337.4 

.2 

855.8 

171.0 

2.76 

.3630 

149.3 

164 

365.3 

337.9 

.3 

855.4 

170.0 

2.74 

.3650 

150.3 

165 

365.7 

338.4 

.5 

855.1 

169.0 

2.72 

.3671 

151.3 

166 

366.2 

338.9 

.6 

854.7 

168.1 

2.71 

.3692 

152.3 

167 

366.7 

339.4 

.8 

854.4 

167.1 

2.69 

.3713 

153.3 

168 

367.2 

339.9 

.9 

854.0 

166.2 

2.68 

.3734 

154.3 

169 

367.7 

340.4 

1194.1 

853.6 

165.3 

2.66 

.3754 

155.3 

170 

368.2 

340.9 

.2 

853.3 

164.3 

2.65 

.3775 

156.3 

171 

368.6 

341.4 

.4 

852.9 

163.4 

2.63 

.3796 

157.3 

172 

369.1 

341.9 

.5 

852.6 

162.5 

2.62 

.3817 

158.3 

173 

369.6 

342.4 

.7 

852.3 

161.6 

2.61 

.3838 

159.3 

174 

370.0 

342.9 

.8 

851.9 

160.7 

2.59 

.3858 

160.3 

175 

370.5 

343.4 

.9 

851.6 

159.8 

2.58 

.3879 

161.3 

176 

371.0 

343.9 

1195.1 

851.2 

158.9 

2.56 

.3900 

162.3 

177 

371.4 

344.3 

.2 

850.9 

158.1 

2.55 

.3921 

163.3 

178 

371.9 

344.8 

.4 

850.5 

157.2 

2.54 

.3942 

164.3 

179 

372.4 

345.3 

.5 

850.2 

156.4 

2.52 

.3962 

165.3 

180 

372.8 

345.8 

.7 

849.9 

155.6 

2.51 

.3983 

166.3 

181 

373.3 

346.3 

.8 

849.5 

154.8 

2.50 

.4004 

167.3 

182 

373.7 

3467 

.9 

849.2 

154.0 

2.48 

.4025 

168.3 

183 

374.2 

347.2 

1196.1 

848.9 

153.2 

2.47 

.4046 

PROPERTIES  OF  STEAM. 


415 


PROPERTIES  OF  SATURATED  STEAM..— Continued. 


Gauge-pressure, 
Pounds  per 
Square  Inch. 

Absolute  Pres- 
sure, Ibs.  per 
Square  Inch. 

I 

££ 
s| 

11 

2L§ 

C   CB 
If 

Total  Heat 
Above  32°  F. 

Latent  Heat  L. 
=  H  -  h, 
Heat-units. 

Relative  Volume. 
Vol.  of  Water 
at39°F.  =  1. 

Volume.  Cubic 
Feet  in  1  Ib.  of 
Steam. 

Weight  of  1 
Cubic  Foot 
Steam,  Ib. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

169.3 

184 

374.6 

347.7 

1196.2 

848.5 

152.4 

2.46 

.4066 

170.3 

185 

375.1 

348.1 

.3 

848.2 

151.6 

2.45 

.4087 

171.3 

186 

375.5 

348.6 

.5 

847.9 

150.8 

2.43 

.4108 

1723 

187 

375.9 

349.1 

.6 

847.6 

150.0 

2  42 

.4129 

173.3 

188 

376.4 

349.5 

.7 

847.2 

149.2 

2.41 

.4150 

174.3 

189 

376.9 

350.0 

.9 

846.9 

148.5 

2.40 

.4170 

175.3 

190 

377.3 

350.4 

1197.0 

846.6 

147.8 

2.39 

.4191 

176.3 

191 

377.7 

350.9 

.1 

846.3 

147.0 

2.37 

.4212 

177.3 

192 

378.2 

351.3 

.3 

845.9 

146.3 

2.36 

.4233 

178.3 

193 

378.6 

351.8 

.4 

845.6 

145.6 

2.35 

.4254 

179.2 

194 

379.0 

352.2 

.5 

845.3 

144.9 

2.34 

.4275 

180.3 

195 

379.5 

352.7 

.7 

845.0 

144.2 

2.33 

.4296 

181.3 

196 

380.0 

353.1 

.8 

844.7 

143.5 

2.32 

.4317 

182.3 

197 

380.3 

353.6 

.9 

844.4 

142.8 

2.31 

.4337 

183.3 

198 

380.7 

354.0 

1198.1 

844.1 

142.1 

2.29 

.4358 

184.3 

199 

381.2 

354.4 

.2 

843.7 

141.4 

2.28 

.4379 

185.3 

200 

381.6 

354.9 

.3 

843.4 

140.8 

2.27 

.4400 

186.3 

201 

382.0 

355.3 

.4 

843.1 

140.1 

2.26 

.4420 

187.3 

202 

382.4 

355.8 

.6 

842.8 

139.5 

225 

.4441 

188.3 

203 

382.8 

356.2 

.7 

842.5 

138.8 

2.24 

.4462 

189.3 

204 

383.2 

356.6 

.8 

842.2 

138.1 

2.23 

.4482 

190.3 

205 

383.7 

357.1 

1199.0 

841.9 

137.5 

2.22 

.4503 

191.3 

206 

384.1 

357.5 

.1 

841.6 

136.9 

2^21 

.4523 

192.3 

207 

384.5 

357.9 

.2 

841.3 

136.3 

2.20 

.4M4 

193.3 

208 

384.9 

358.3 

.3 

841.0 

135.7 

2.19 

.4564 

194.3 

209 

385.3 

358.8 

.5 

840.7 

135.1 

2.18 

.4585 

195.3 

210 

385.7 

359.2 

.6 

840.4 

134.5 

2.17 

.4605 

196.3 

211 

386.1 

359.6 

.7 

840.1 

133.9 

2.16 

.4626 

197.3 

212 

386.5 

360.0 

.8 

839.8 

133.3 

2.15 

.4646 

198.3 

213 

386.9 

360.4 

.9 

839.5 

132.7 

2.14 

.4667 

199.3 

214 

387.3 

360.9 

1200.1 

839.2 

132.1 

2.13 

.4687 

200.3 

215 

3877 

361.3 

.2 

838.9 

131.5 

2  12 

.4707 

201.3 

216 

388.1 

361.7 

.3 

838.6 

130.9 

2  12 

.4728 

202.3 

217 

388.5 

362.1 

.4 

838.3 

130.3 

2.11 

.4748 

203.3 

218 

388.9 

362.5 

.6 

838.1 

129.7 

2.10 

.4768 

204.3 

219 

389.3 

362.9 

.7 

837.8 

129.2 

2.09 

.4788 

205.3 

220 

389.7 

362.2 

1200.8 

838.6* 

128.7 

2.06 

.4852 

215.3 

230 

393.6 

366.2 

1202.0 

835.8 

123.3 

1.98 

.5061 

225.3 

240 

397.3 

370.0 

1203.1 

833.1 

118.5 

1.90 

.5270 

235.3 

250 

400.9 

373.8 

1204.2 

830.5        114.0 

1.83 

.5478 

245.3 

260 

404.4 

377.4 

1205.3 

827.9 

109.8 

1.76 

.5686 

255.3 

270 

407.8 

380.9 

1206.3   |     825.4 

105.9 

1.70 

.5894 

265.3 

280 

411.0 

384.3 

1207.3 

823.0 

102.3 

1.64 

.6101 

275.3 

290 

414.2 

'387.7 

1208.3 

820.6 

99.0 

1.585 

.6308 

285.3 

300 

417.4 

390.9 

1209.2        818.3 

95.8 

1.535 

.6515 

335.3 

350 

4320 

406.3 

1213.7        807.5 

82.7 

1.325 

.7545 

*  The  discrepancies  at  205.3  Ibs.  gauge  are  due  to  the  change  from  Dwelshauvers-Dery's 
to  Duel's  figures. 


416 


STEAM-BOILER  ECONOMY. 


PROPERTIES    OF    SATURATED    STEAM.— 


oT 

Total  Heat 

S 

O.M 

21     j.; 

to  aS-fl 

. 

Above  35J°  F. 

^ 

S  4J« 

"5  ° 

1|  = 

cUS 

£'£ 

**••§ 

||   II 

3.g 

"8-0 

*•  w  c 

g)J3  » 

§+jp3 

In  the 

In  the 

ffi     S 

«t-^ 

.  c   • 

*c  b**" 

*?0  £5 

"S^-eS 

Water. 

Steam. 

«    5 

>  °° 

§-§ 

5-2  § 

lit 

lit 

a| 

h 
Heat- 

H 
Heat- 

SB! 

|g"5 

III 

||| 

O 

<J 

1 

units. 

units. 

>3 

§  ' 

^ 

^Oc 

385.3 

400 

444.9 

4198 

1217.7 

797.9 

72.8 

1.167 

.8572 

435.3 

450 

456.6 

432.2 

1221.3 

789.1 

65.1 

1.042 

.9595 

485.3 

500 

467.4 

443.5 

1224.5 

781.0 

58.8 

.942 

1.062 

535.3 

550 

477.5 

454.1 

1227.6 

773.5 

53.6 

.859 

1.164 

585.3 

600 

486.9 

464.2 

1230.5 

766.3 

49.3 

.790 

1.266 

635.3 

650 

495.7 

473.6 

1233.2 

759.6 

45.6 

.731 

1.368 

685.3 

700 

504.1 

482.4 

1235.7 

753.3 

42.4 

.680 

1.470 

735.3 

750 

512.1 

490.9 

1238.0 

747.2 

39.6 

.636 

1.572 

785.3 

800 

519.6 

498.9 

1240.3 

741.4 

37.1 

.597 

1.674 

835.3 

850 

526.8 

506.7 

1242.5 

735.8 

34.9 

.563 

1.776 

885.3 

900 

533.7 

514.0 

1244.7 

730.6 

33.0 

.532 

1.878 

935.3 

950 

540.3 

521.3 

1246.7 

725.4 

31.4 

.505 

1.980 

985.3 

1000 

546.8 

528.3 

1248.7 

720.3 

30.0 

.480 

2.082 

FACTORS  OF  EVAPORATION. 

The  table  on  the  following  pages  was  originally  published  by  the 
author  in  Trans.  A.  S.  M.  E.  vol.  vi.,  1884.  It  gives  the  factors  for 
every  3°  of  temperature  of  feed-water  from  32°  to  212°  F.,  and  for 
every  two  pounds  pressure  of  steam  within  the  limits  of  ordinary  work- 
ing steam-pressures. 

The  difference  in  the  factor  corresponding  to  a  difference  of  3° 
temperature  of  feed  is  always  either  .0031  or  .0032.  For  interpolation 
to  find  a  factor  for  a  feed-water  temperature  between  32°  and  212°, 
not  given  in  the  table,  take  the  factor  for  the  nearest  temperature 
and  add  or  subtract,  as  the  case  may  be,  .0010  if  the  difference  is 
.0031,  and  .0011  if  the  difference  is  .0032.  As  in  nearly  all  cases  a 
factor  of  evaporation  to  three  decimal  places  is  accurate  enough,  any 
error  which  may  be  made  in  the  fourth  decimal  place  by  interpolation 
is  of  no  practical  importance. 

The  tables  used  in  calculating  these  factors  of  evaporation  are 
those  given  .in  Charles  T.  Porter's  Treatise  on  the  Bichards'  Steam- 


engine  Indicator.     The  formula  is  Factor  = 


H-h 
965.' 


,  in  which  H  is  the 


total  heat  of  steam  at  the  observed  pressure,  and  li  the  total  heat  of 
feed-water  of  the  observed  temperature. 


PROPERTIES  OF  STEAM. 


417 


Lbs. 
Gaugre-pressnres,  0+ 
Auoolute  press.,      15 

10+ 

25 

20  + 

35 

30  + 

45 

40  + 
55 

45  + 
60 

50  + 
65 

52  + 
67 

54  + 

t>y 

56  + 
71 

Feed-water 
Temp. 

FACTORS  OF  EVAPORATION. 

21  2°  F. 

1.0003,1.00881.0149 

1.0197 

1.0237 

1  .  0254 

1.0271  1.0277  11.0283  1.0290 

209 

351.0120 

80 

1.0228 

68 

86 

1.0302 

1  .  0309 

1.0315 

1.0321 

206 

66 

51 

1.0212 

60 

99 

1.0317 

34 

40 

46 

52 

203 

98 

83 

43 

91 

1.0331 

49 

65'        72 

78 

84 

200 

1.0129 

1.0214 

75 

1.0323 

62 

80 

97 

1.0403 

1.0409 

1.0415 

197 

60 

46 

1.0306 

54 

94 

1.0412 

1.0428 

34 

41 

47 

194 

92 

77 

38 

85 

1.0425 

43 

60 

66 

72 

78 

191 

1.0223 

1.0308 

69 

1.0417 

57 

74 

91 

97 

1.0503 

1.0510 

188 

55 

40 

1.0400 

48 

88 

1.0506 

1.0522 

1.0528 

35 

41 

185 

86 

71 

32 

80 

1.0519 

37 

54 

60 

66 

72 

182 

1.0317 

1.0403 

63 

1.0511 

51 

68 

85 

91 

98 

1.0604 

179 

49 

34 

95 

42 

82 

1.0600 

1.0616 

1.0623 

1.0629 

35 

176 

80 

65 

1.0526 

74 

1.0613 

31 

'48 

54 

60 

66 

173 

1.0411 

97 

57 

1.0605 

45 

63 

79 

85 

92 

98 

170 

43 

1.0528 

89 

36 

76 

94 

1.0710 

1.0717 

1.0723 

1.0729 

167 

74 

59 

1.0620 

68 

1.0707 

1.0725 

42 

48 

54 

60 

164 

1.0505 

91 

51 

99 

39 

56 

73 

80 

86|        92 

161 

37 

1.0622 

82 

1.0730 

70 

88 

1.0804 

1.0811 

1.0817'  1.0823 

158 

68 

53 

1.0714 

62 

1.0801 

1.0819 

36 

42 

48 

54 

155 

99 

84 

45 

93 

33 

50 

67 

73 

80 

86 

152 

1.0631 

1.0716 

76 

1.0824 

64 

82 

98 

1.0905 

1.0911 

1.0917 

149 

62 

47 

1.0808 

55 

95 

1.0913 

1.0930 

36 

42 

48 

146 

93 

78 

39 

87 

1.0926 

44 

61 

67 

73 

79 

143 

1.0724 

1.0810 

70 

1.0918 

58 

75 

92 

98 

1.1005 

1.1011 

140 

56 

41  1.0901 

49 

89 

1  .  1007 

1.1023 

1.1030 

36 

42 

137 

87 

72         33 

80 

1.1020 

38 

55         61 

67 

73 

134 

1.0818 

1.0903 

64 

1.1012 

51 

69 

86 

92 

98 

1.1104 

131 

49 

34 

95 

43 

83 

1.1100 

1.1117 

1.1123 

1.1130 

36 

128 

81 

66 

1.1026 

74 

1.1114 

32 

48 

55 

61 

67 

125 

1.0912 

97 

57 

1.1105 

45 

63 

79 

86 

92 

98 

122 

43 

1.1028 

89 

36 

76 

94 

1.1211 

1.1217 

1.1223 

1.1229 

119 

74 

59 

1.1120 

68 

1.1207 

1.1225 

42 

48 

54 

60 

116 

1  .  1005 

90 

51 

99 

39 

56 

73 

79 

86 

92 

113 

36 

1.1122 

82 

1.1230 

70 

88 

1.1304 

1.1310 

1.1317 

1.1323 

110 

68 

53 

1.1213 

61 

1.1301 

1.1319 

35 

42 

48 

54 

107 

99 

84 

45 

92 

32 

50 

66 

73 

79 

85 

104 

1.1130 

1.1215 

76 

1.1323 

63 

81 

98 

1.1404 

1.14101.1410 

101 

61 

46 

1.1307 

55 

94 

1.1412 

1.1429 

35 

41 

47 

98 

92 

77 

38 

86 

1.1426 

43 

60 

66 

73 

79 

95 

1  .  1223 

1.1309 

69 

1.1417 

57 

75 

91 

97 

1.1504 

1.1510 

92 

55 

40 

1.1400 

48 

88 

1.1506 

1.1522 

1.1529 

35 

41 

89 

86 

71 

31 

79 

1.1519 

37 

53 

60 

66 

72 

86 

1.1317 

1  .  1402 

63 

1.1510 

50 

68 

84 

91 

971.1608 

83 

48 

33 

94 

41 

'  81 

99 

1.1616 

1.1622 

1.1628 

34 

80 

79 

64 

1.1525 

73 

1.1612 

1.1630 

47 

53 

59 

65 

77 

1.1410 

95 

56 

1.1604 

44 

61 

78 

84 

90 

96 

74 

41 

1.1526 

87 

35 

75 

92 

1.1709 

1.1715 

1.1722 

1.1728 

71 

72 

581.1618 

66 

1.1706 

1.1723 

40 

46 

53 

59 

68 

1.1504 

89!         49 

97 

37 

55 

71 

78 

84 

90 

65 

35 

1  .  1620 

80 

1.1728 

68 

86 

1.1802 

1.1809 

1.1815 

1.1821 

62 

66 

51 

1.1711 

59 

99 

1.1817 

33 

40 

'  46 

52 

59 

97 

82'        43!        90 

1.1830 

48 

64 

71 

77 

83 

418 


STEAM-BOILER  ECONOMY. 


Gauge-press.,  Ibs.  584 
Absolute  press  ...73 

GO  + 
75 

62  + 

77 

79  + 

66  + 

81 

68  + 
83 

70  + 

85 

87  + 

S  + 

76  + 
91 

FACTORS  OF  EVAPORATION. 


212°  F. 

1.0295 

1.0301 

1.0307 

1.0312 

1.0318 

1.0323 

1.0329 

I  .  0384 

1.033911.0344 

209 

1.0327 

33 

38 

44 

49 

55 

60 

65 

70 

75 

206 

58 

64 

70 

75 

81 

86 

91 

97 

1.0402 

1.0407 

203 

90 

96 

1.0401 

1.0407 

1.0412 

1.0418 

1.0423 

1.0428 

33 

38 

200 

1.0421 

1.0427 

33 

38 

44 

49 

54 

59 

65 

69 

197 

53 

58 

64 

70 

75 

80 

86 

91 

96 

1.0501 

194 

84 

90 

96 

1.0501 

1.0507 

1.0512 

1.0517 

1.0522 

1.0527 

32 

191 

1.0515 

1.0521 

1.0527 

33 

38 

43 

49 

54 

59 

64 

188 

47 

53 

58 

64 

69 

75 

'80 

85 

90 

95 

185 

78 

84 

90 

95 

1.0601 

1.0606 

1.0611 

1.0616 

1  .0622 

1.0626 

182 

1.0610 

1.0615 

1.0621 

1.0627 

32 

37 

43 

48 

53 

58 

179 

41 

47j 

k   52 

58 

63 

69 

74 

79 

84 

89 

176 

72 

78 

84 

89 

95 

1.0700 

1.0705 

1.0711 

1.0716 

1.0721 

173 

1.0704 

1.0709 

1.0715 

1.0721 

1.0726 

32 

37 

42 

47 

52 

170 

35 

41 

46 

52 

57 

63 

68 

73 

78 

83 

167 

66 

72 

78 

83 

89 

94 

99 

1.0805 

1.0810 

1.0815 

164 

98 

1.0803 

1.0809 

1.0815 

1.0820 

1.0825 

1.0831 

36 

41 

46 

161 

1.0829 

35 

40 

46 

51 

57 

62 

67 

72 

77 

158 

60 

66 

72 

77 

83 

88 

93 

98 

1.0904 

1.0908 

155 

92 

97 

1.0903 

1.0909 

1.0914 

1.0919 

1.0925 

1.0930 

35 

40 

152 

1.0923 

1.0929 

34 

40 

45 

51 

56 

61 

66 

71 

149 

54 

60 

66 

71 

77 

82 

87 

92 

97 

1  .  1002 

146 

85 

91 

97 

1.1002 

1.1008 

1.1013 

1.1018 

1.1024 

1.1029 

34 

143 

1.1017 

1.1022 

1.1028 

34 

39 

44 

50 

55 

60 

65 

140 

48 

54 

59 

65 

70 

76 

81- 

86 

91 

96 

137 

79 

85 

91 

96 

1.1102 

1.1107 

1.1112 

1.1117 

1.1122 

1.1127 

134 

1.1110 

1.1116 

1.1122 

1.1127 

33 

38 

43 

49 

54 

59 

131 

42 

47 

53 

59 

64 

69 

75 

80 

85 

90 

128 

73 

79 

84 

90 

95 

1.1201 

1.1206 

1.1211 

1.1216 

1.1221 

125 

1.1204 

1.1210 

1.1215 

1.1221 

1.1226 

32 

37 

42 

47 

52 

122 

35 

41 

47 

52 

58 

63 

68 

73 

78 

83 

119 

66 

72 

78 

83 

89 

94 

99 

1.1305 

1.1310 

1.1315 

116 

98 

1.13031.1309 

1.1315 

1.1320 

1.1325 

1.1331 

36 

41 

46 

113 

1.1329 

34    40 

46 

51 

57 

62 

67 

72 

77 

110 

60 

66    71 

77 

82 

88 

93 

98 

1.1403 

1.1408 

107 

91 

97 

1.1403 

1.1408 

1.1414 

1.1419 

1.1424 

1.1429 

34 

39 

104 

1.1422 

1.1428 

34 

39 

45 

50 

55 

60 

65 

70 

101 

53 

59 

65 

70 

76 

81 

.   86 

92 

97 

1.1502 

;  98 

85 

90 

90 

1.1502 

1.1507 

1.1512 

1.1518 

1.1523 

1.1528 

33 

(  95 

1.1516 

1.1521 

1.1527 

33 

38 

43 

49 

54 

59 

64 

92 

47 

53 

58 

64    69 

75 

80 

85 

90 

95 

89 

78 

84 

89 

951.1600 

1.1606 

1.1611 

1.1616 

1.1621 

1.1626 

86 

1.1609 

1.1615 

1.1621 

1.1626    32 

37 

42 

47 

52 

57 

83 

40 

46 

52 

57    63 

68 

73 

78 

83 

88 

80 

71 

77 

83 

88    94 

99 

1.1704 

1.1710 

1.1715 

1.1720 

77 

1.1702 

1.1708 

1.1714 

1.17191.  1725 

1.1730 

35 

41 

46 

51 

74 

34 

39 

45 

51    56 

61 

67 

72 

77 

82 

71 

65 

70 

76 

82:    87 

92 

98 

1.1803 

1.1808 

1.1813 

68 

96 

1  .  1802 

1.1807 

1.18131.1818 

1.1824 

1.1829 

34 

39 

44 

65 

1.1827 

33 

38 

44    49 

55 

60 

65 

70 

75 

62 

58 

64 

69 

75    80 

86 

91 

96 

1.1901 

1.1906 

59 

89 

95 

1.1901 

1.19061.1912 

1.1917 

1.1922  1.1  927'    32!    37 

FACTORS  OF  EVAPORATION. 


419 


<}auge  press., 
Ibs.,  78  + 
Absolute 
Pressures,  93 

80  + 
95 

82  + 
97 

84  + 
00 

86  + 
101 

88  + 
103 

90  + 
105 

10? 

94  + 
109 

96  + 
111 

98  + 
113 

Feert- 
•Te'.np. 

FACTORS  OP  EVAPORATION. 

2i2 

1.0349 

1  .  035:' 

.  0358 

1.0363 

1.0367 

1  .  0372 

1.0376 

1.0381 

1.0385  1.0389 

1.0393 

209 

8U 

8;'; 

90 

94 

99 

1.0403 

1.0408 

1.0412 

1.0416:1.0421 

1.0425 

206 

1.0411 

1.04U 

1.0421 

r.0426 

1.0430 

35 

.39 

43 

48         52 

56 

208 

43 

4b 

52 

57 

62 

66 

71 

75 

79!         83 

88 

200 

74 

7ij 

84 

89 

93 

98 

1.0502 

1  .  0506 

1.0511 

U0515 

1.0519 

197 

1.0506 

1.0511 

1.0515 

1.0520 

1.0525 

1.0529 

33 

38 

42 

46 

50 

194 

3? 

42 

47 

51 

56 

60 

65          69 

73         78 

82 

191 

69 

73 

78 

83 

87 

92 

96 

1.0601 

1.06051.0609 

1.0613 

188 

1.0600 

1.0605 

1.0610 

1.0614 

1.0619 

1.06.3 

1.0628 

32 

36!         40 

45 

185 

31 

36 

41 

46 

50 

55 

59 

63 

68j         72 

76 

182 

63 

68 

72 

7^ 

81 

86 

90 

95 

99 

1.0703 

1.0707 

179 

94 

99 

1.0705 

1.0708 

1.0713 

1.0717 

1.0722 

1.0726 

1.0730 

35 

89 

176 

1.0725 

1.0730 

35 

40         44 

49 

53 

51; 

62 

66 

70 

173 

57 

62 

66 

71         75 

80 

84 

89 

93 

97 

1.0801 

170 

88 

93 

98 

1.0802 

1.0307 

1.0811 

1.0816 

1.0820 

1.0824 

1.0829 

33 

167 

1.0819 

1.0824 

1.0829 

34 

38 

48 

47 

51 

56 

60 

64 

164 

5! 

56 

60 

65 

69 

74 

78 

83 

87 

91 

95 

161 

82 

87 

92 

961.0901 

1.0905 

1.0910 

1.0914 

1.0918 

1.0923 

1.0927 

158 

1.0913 

1.0918 

1.0923 

1.0927         32 

37 

41 

45 

50 

54 

58 

155 

45 

49 

54 

59         63 

68 

72 

77 

81 

85 

89 

152 

76 

81 

85 

90         95 

99 

1.1004 

1.1008 

1.1012 

1.1016 

1.1021 

149 

1  .  1007 

1.1012 

1.1017 

1.1021 

1.1026 

1.1030 

35 

39 

43 

48 

52 

14<5            38 

43 

48 

53         57 

62 

66 

70 

75 

79 

83 

143  >         70 

74 

7l> 

84:         88 

93 

97 

1.1102 

1.1106 

1.1110 

1.1114 

140    1.1101 

1.1106 

1.1110 

?.  11151.  1120 

1.1124 

1.1129 

33 

87 

41 

46 

137 

32 

37 

42 

46|         51 

55 

60 

64 

68 

73 

77 

134 

63 

68 

73 

78         82 

87 

91 

95 

1.1200 

1.1204 

1.1208 

181 

95 

99 

1.1204 

1.1209:1.1213 

1.1218 

1.1222 

1.1227 

31 

35 

89 

128 

1.1220 

1  .  1281 

35 

40  j        45 

49 

53 

58 

62 

6(5 

71 

125            57 

62 

67 

711         76 

80 

85 

89 

93 

98 

1.1302 

122            88 

98 

981.1302J  1.1307 

1.1311 

1.1316 

1.1320 

1.1325 

1.1329 

33 

119 

1  .  1320 

1.1324 

1.1329 

34 

08 

48 

47 

51 

56 

60 

64 

116 

51 

55 

60 

65 

69 

74 

78 

83 

87 

91 

95 

113           82 

87 

91 

96 

1.1401 

1.1405 

1.1409 

1.1414 

1.1418 

1.1422 

1.1426 

110    1.1418 

1.1418 

1.1422 

1.1427 

82 

36 

41 

45 

49 

53 

58 

107           44 

49 

54 

58 

63 

67 

72 

76 

80 

85 

89 

104  :         75 

80 

85 

89 

94 

99 

1.1503 

1.1507 

1.1512 

1.1516 

1.1520 

101  tl.1506 

1.1511 

1.1516 

1.1521 

1.1525 

1.1530 

34 

38 

48 

47 

51 

98  !         38 

42 

47 

52 

56 

61 

65 

70 

74 

78 

82 

95           69 

74 

78 

83 

87 

9; 

96 

1.1601 

1.1605 

1  .  1609 

1.1613 

92    1.1600 

1  .  1605 

1.1609 

1.1614 

1.1619 

1.1623 

1.1628 

32 

36 

40 

45 

89 

31 

36 

41 

45 

50 

54 

59 

63 

67 

72 

76 

86 

62 

(51 

72 

76 

81 

85 

90 

94 

98 

1.1703 

1.1707 

88            91} 

98 

1.1703 

1.1707 

1.1712 

1.1717 

1.1721 

1.1725 

1.1730 

84 

88 

80    1.1724 

1.1729 

34 

39 

43 

48 

52 

56 

61 

65 

69 

77           5(i 

60 

65 

70 

74 

79 

88 

88 

92 

96 

1.1800 

74           8 

91 

9 

1.1801 

1.1805 

1.1810 

1.1814 

1.1819 

1.1823 

1.1827 

31 

71    1.1818 

1.182-, 

1  .  1827 

32 

36 

41 

45 

50 

54 

58 

62 

68           49 

5-1 

58 

63 

68 

72 

7  1 

81 

85 

89 

94 

65 

80 

85 

89 

94 

99 

1.1903 

1.1908 

.1912 

1.1916 

1.1920 

1  .  1925 

62 

1.1911 

1.1916 

1.1921 

1.1925 

1  .  1930 

34 

39 

43 

47 

52 

56 

59 

42 

47 

52 

56 

61 

65 

70 

74 

78 

83 

87 

420 


STEAM-BOILER  ECONOMY. 


Gauge-press 
lbs...lOO-f 
Absolute 
Press  ..115 

105  + 
120 

no  4- 

125 

115  -f 
130 

120  + 
135 

1254- 
140 

130  4- 
145 

135  4- 
150 

140  + 
155 

145  4- 
1CO 

150  4- 
165 

Feed- 
water 
Temp. 

FACTORS  OF  EVAPORATION. 

212° 

1.0397 

1.0407 

]  .0417 

1.0427 

1.0436 

1.0445 

1.0453 

1.0462 

1.0470 

1.0476 

1.0486 

209 

1.0429 

39 

49 

58 

67 

76 

85 

98 

1.0501 

1.0509 

1.0517 

206 

60 

70 

80 

89 

99 

1.0508 

1.0516 

1.0525 

33 

41 

48 

203 

92 

1.050-J 

1.0511 

1.0521 

1.0530 

39 

48 

56 

64 

72 

80 

200 

1.0523 

33 

43 

52 

62 

70 

79 

87 

96 

1.0604 

1.0611 

197 

55 

65 

74 

84 

93 

1.0602 

1.0610 

1.0619 

1.0627 

35 

43 

194 

86 

96 

1.0606 

1.0615 

1.0624 

33 

42 

50 

58 

66 

74 

191 

1.061? 

1.0627 

3? 

47 

56 

65 

73 

82 

90 

98 

1.0706 

188 

49 

59 

69 

78 

87 

96 

1.0705 

1.0713 

1.0721 

1.0729 

37 

185 

80 

90 

1.0700 

1.0709 

1.0719 

1.0727 

36 

44 

53 

61 

68 

182 

1.0712 

1.0722 

31 

41 

50 

59 

67 

76 

84 

92 

1.0800 

179 

43 

53 

63 

72 

81 

90 

99 

1.0807 

1.0815 

1.0823 

31 

176 

74 

84 

94 

1.0803 

1.0813 

1.0821 

1.0830 

39 

47 

55 

62 

173 

1.0806 

1.0816 

1.0825 

35 

44 

53 

61 

70 

78 

86 

94 

170 

37 

47 

57 

66 

75 

84 

93 

1.0901 

1.0909 

1.0917 

1.0925 

167 

68 

78 

88 

97 

1.0907 

1.0915 

1.0924 

32 

41 

49 

5fr 

164 

1.0900 

1.0910 

1.0919 

1.0929 

38 

47 

55 

64 

72 

80 

88 

161 

31 

41 

51 

60 

69 

78 

87 

95 

1.1003 

1.1011 

1.1019 

158 

62 

72 

82 

91 

1  .  1000 

1.1009 

1.1018 

1.1026 

35 

43 

50 

155 

93 

1.1003 

1.1013 

1.1023 

32 

41 

49 

58 

66 

74 

82 

152 

1.1025 

35 

44 

54 

63 

72 

81 

89 

97 

1.1105 

1.1113 

149 

58 

66 

76 

85 

94 

1.1103 

1.1112 

1.1120 

1.1128 

36 

44 

146 

87 

97 

1.1107 

1.1116 

1.1126 

84 

43 

51 

60 

68 

75 

143 

1.1118 

1.1129 

38 

48 

57 

66 

74 

83 

91 

99 

1.1207 

140 

50 

60 

70 

79 

88 

97 

1.1206 

1.1214 

1  .  1222 

1.1230 

38 

137 

81 

91 

1.1201 

1.1210 

1.1219 

1.1228 

37 

45 

53 

61 

69 

134 

1.1212 

1.1222 

32 

41 

51 

59 

68 

76 

85 

93 

1.1300 

131 

43 

53 

63 

73 

82 

91 

99 

1.1308 

1.1316 

1.1324 

32 

128 

75 

85 

94 

1.1304 

1.1313 

1.1322 

1.1331 

39 

47 

55 

63- 

125 

1.1306 

1.1316 

1.1326 

35 

44 

53 

62 

70 

78 

86 

94 

122 

37 

47 

57 

66 

75 

84 

93 

1.1401 

1.1409 

1.1417 

1.1425 

119 

68 

78 

88 

97 

1.1407 

1.1415 

1.1424 

32 

41 

49 

56 

116 

99 

1  .  1409 

1.1419 

1.1429 

38 

47 

55 

64 

72 

80 

88 

113 

1.1431 

41 

50 

60 

69 

78 

86 

95 

1.1503 

1.1511 

1.1519 

110 

62 

72 

82 

91 

1.1500 

1.1509 

1.1518 

1.1526 

34 

42 

50 

107 

93 

1.1503 

1.1513 

1.1522 

31 

40 

49 

57 

65 

73 

81 

104 

1.1524 

34 

44 

53 

62 

71 

80 

88 

97 

I  .  1605 

1.1612 

101 

55 

65 

75 

84 

94 

1.1602 

1.1611 

1.1620 

1.1628 

36 

43 

98 

86 

96 

1.1606 

1.1616 

1.1625 

34 

42 

51 

59 

67 

75 

95 

1.1618 

1.1628 

37 

47 

56 

65 

73 

82 

90 

98 

1.1706 

92 

49 

59 

68 

78 

87 

96 

1.1705 

1.1713 

1.1721 

1.1729 

37 

89 

80 

90 

1.1700 

1  .  1709 

1.1718 

1.1727 

36 

44 

52 

60 

68 

86 

1.1711 

1.1721 

31 

40 

49 

58 

67 

75 

83 

91 

99 

83 

42 

52 

62 

71 

80 

89 

98 

1.1806 

1.1815 

1.1823 

1.1830 

80 

73 

83 

93 

1.1802 

1.1812 

1.1820 

1.1829 

37 

46 

54 

61 

77 

1.1804 

1.1814 

1.1824 

34 

43 

52 

60 

69 

77 

85 

93 

74 

35 

45 

55 

65 

74 

83 

91 

1.1900 

1.1908 

1.1916 

1.1924 

71 

67 

77 

86 

96 

1.1905 

1.1914 

1.1922 

31 

39 

47 

55 

68 

98 

1.1908 

1.1917 

1.1927 

36 

45 

54 

62 

70 

78 

86 

65 

1.1929 

39 

49 

58 

07 

76 

85 

93 

1.2001 

1.2009 

1.2017 

62 

60 

70 

80 

89 

98 

1.2007 

1.2016 

1.2024 

32 

40 

48 

59 

91 

1.2001 

1.2011 

1.2020 

1.2029 

38 

47 

55 

63 

71 

79 

FACTORS  OF  EVAPORATION 


421 


Lbs. 

Gauge  pressures,  0+ 

10  + 

20  + 

30  + 

40   + 

45  + 

50   -f 

52  + 

54  + 

50  + 

Absolute  press...  15 

25 

35 

45 

55 

60 

65 

67 

69 

71 

Feed-water 
Temp. 

FACTORS  OF  EVAPORATION. 

56°  F. 

1.1628 

1.1713 

1.1774 

1.1821 

1.1861 

1.1879 

1.1896 

1.1902 

1.1908 

1.1914 

53 

59 

44 

1.1805 

52 

921.1910 

1.1927 

33 

b9 

45 

50 

90 

75 

36 

84 

1.1923 

41 

58 

64 

70 

76 

47 

1.1721 

1  .  1806 

67 

1.1915 

54 

72 

89 

95 

1.2001 

1.2007 

44 

52 

37 

98 

46 

8611.2003 

1.2020 

1.2026 

32 

39 

41 

83 

68 

1.1929 

77 

1.2017 

34 

51 

57 

64 

70 

38 

1.1814 

1  .  1900 

60 

1.2008 

48 

65 

82 

88 

95 

1.2101 

35 

45 

31 

91 

39 

79 

96 

1.2113 

1.2119 

1.2126 

32 

32 

76 

62 

1.2022 

70 

1.2110 

1.2128 

44 

51 

57 

63 

•Gauge-press.  .  1  bs.58  + 
Absolute  press  73 

ta+ 

62  + 

77 

64  + 

79 

66  + 
81 

68  + 
83 

70  + 

85 

72  + 

87 

74  + 
89 

76  + 
91 

56° 

1.1920 

1  .  1926 

1.1932 

1.1937 

1.1943 

1.1948 

1.1953 

1  .  1958 

1.1963 

1.1968 

53 

51 

57 

63 

68 

74 

79 

84 

89 

94 

99 

50 

82 

88 

94 

99 

1.2005 

1.2010 

1.2015 

1.2021 

1.2026 

1.2031 

47 

1.2013 

1.2019 

1.2025 

1.2030 

86 

41 

46 

52 

57 

62 

44 

44 

50 

56 

61 

67 

72 

78 

83 

88 

93 

41 

76 

81 

87 

93 

98 

1.2103 

1.2109 

1.2114 

1.2119 

1.2124 

38 

1.2107 

1.2112 

1.2118 

1.2124 

1.2129 

34 

40 

45 

50 

55 

35 

38 

43 

49 

55 

60 

65 

71 

76 

81 

86 

32 

69 

75 

80 

86 

91 

97 

1.2202 

1.2207 

1.2212 

1.2217 

•Gauge-press., 
lbs....78  + 
Absolute 
Press  ....  93 

80  + 
95 

82  + 
97 

84  + 
99 

86  +• 
101 

88  + 
103 

90  + 
105 

92  + 
107 

94  + 
109 

96  + 

111 

98  + 
113 

56° 
53 
50 
47 
44 
41 
38 
35 
32 

1.1973 
1.2004 
35 
66 
98 
1.2129 
60 
91 
1.2222 

1.1978 
1.2009 
40 
71 
1.2102 
33 
64 
96 
1.2227 

1.1983 
1.2014 
45 
76 
1.2107 
38 
69 
1.2200 
31 

1.1987 
1.2018 
50 
81 
1.2112 
43 
74 
1.2205 
36 

1.1992 
1.2023 
54 
85 
1.2116 
47 
78 
1.2209 
41 

1.1996 
1.2028 
59 
90 
1.2121 
52 
83 
1.2214 
45 

1.2001 
32 
63 
94 
1.2125 
56 
87 
1.2218 
49 

1.2005 
36 
67 
98 
1.2130 
61 
92 
1.2223 
54 

1.2010 
41 
72 
1.2103 
34 
65 
96 
1.2227 
58 

1.2014 
45 
76 
1.2107 
38 
69 
1.2200 
31 
62 

1.2018 
49 
80 
1.2111 
42 
73 
1.2204 
35 
67 

•Gauge-press., 
Ibs.      100  -r 
Absolute 
press..  .  115 

105  + 
120 

110  + 
125 

1  2042 
73 
1.2104 
35 
66 
97 
1.2228 
59 
90 

115  + 
130 

120  + 
135 

125  + 
140 

130  + 
145 

135  + 
150 

140  + 
155 

145  + 
160 

1.2102 
34 
65 
96 
1.2227 
58 
89 
1.2320 
51 

150  + 
165 

1.2110 
41 
72 
1.2203 
35 
66 
97 
1.2328 
59 

56° 
53 
50 
47 
44 
41 
38 
35 
32 

1.2022 
53 
84 
1.2115 
46 
77 
1.2208 
40 
71 

1.2032 
63 
94 
1.2125 
56 
87 
1.2219 
50 
81 

1.2051 
82 
1.2113 
44 
76 
1.2207 
38 
69 
1.2300 

1.2060 
91 
1.2123 
54 
85 
1.2216 
47 
78 
1.2309 

1.2069 
1.2100 
31 
63 
94 
1.2225 
56 
87 
1.2318 

1.2078 
1.2109 
40 
71 
1.2202 
33 
64 
95 
1.2326 

1.2086 
1.2117 
48 
80 
1.2211 
42 
73 
1.2304 
35 

1.2094 
1.2126 
57 
88 
1.2219 
50 
81 
1.2312 
43 

422  STEAM-BOILER  ECONOMY. 

Chimney-draft  Theory..  —  The  commonly  accepted  theory  of 
chimney-draft,  based  on  Peclet's  and  Rankine's  hypotheses  (see 
Rankine's  Steam-engine),  is  discussed  by  Prof.  De  Volson  Wood  in 
Trans.  A.  S.  M.  E.,  vol.  xi. 

Peclet  represented  the  law  of  draft  by  the  formula 


in  which  li  is  the  "  head,"  defined  as  such  a  height  of  hot  gases  as,  if 
added  to  the  column  of  gases  in  the  chimney,  would 
produce  the  same  pressure  at  the  furnace  as  a  column  of 
outside  air,  of  the  same  area  of  base,  and  a  height  equal 
to  that  of  the  chimney; 
u  is  the  required  velocity  of  gases  in  the  chimney; 

0  a  constant  to  represent  the  resistance  to  the  passage  of  air 

through  the  coal; 

1  the  length  of  the  flues  and  chimney; 

m  the  mean  hydraulic  depth,  or  the  area  of  a  cross-section 

divided  by  the  perimeter; 

f.  a  constant  depending  upon  the  nature  of  the  surfaces  over 
which  the  gases  pass,  whether  smooth,  or  sooty  and 
rough. 

Rankine's   formula    (Steam-engine,   p.    288),   derived    by   giving 
certain  values  to  the  constants  (so-called)  in  Peclet's  formula,  is 


Il  (0.0807) 

-2 H  -  H  = 


-r°  (0.084) 

in  which  H  =  the  height  of  the  chimney  in  feet ; 

TO  =  493°  F.,  absolute  (temperature  of  melting  ice); 
TJ  =  absolute  temperature  of  the  gases  in  the  chimney; 
r2  =  absolute  temperature  of  the  external  air. 

Prof.  Wood  derives  from  this  a  still  more  complex  formula  which 
gives  the  height  of  chimney  required  for  burning  a  given  quantity  of 
coal  per  second,  and  from  it  he  calculates  the  following  table,  showing- 
the  height  of  chimney  required  to  burn  respectively  24,  20,  and  16  Ibs. 
of  coal  per  sq.  ft.  of  grate  per  hour,  for  the  several  temperatures  of  the 
chimney-gases  given. 

Rankine's  formula  gives  a  maximum  draft  when  r  =  21/12r2,  or 
622°  F.,  when  the  outside  temperature  is  60°.  Prof.  Wood  says: 
"  This  result  is  not  a  fixed  value,  but  departures  from  theory  in  prac- 
tice do  not  affect  the  result  largely.  There  is,  then,  in  a  properly 
constructed  chimney,  properly  working,  a  temperature  giving  a  maxi- 
mum draft,*  and  that  temperature  is  not  far  from  the  value  given  by 
-Rankine,  although  in-special  cases  it  may  be  50°  or  75°  more  or  less." 

*  Much  confusion  to  students  of  the  theory  of  chimneys  has  resulted  from  their 
understanding  the  words  maximum  draft  to  mean  maximum  intensity  or  pres- 


CHIMNEYS. 


423 


Chimney-gas. 

Coal  per  Square  Foot  of  Grate  per  Hour,  Ibs. 

Outside  Air. 

24                            20                            16 

T2 

Tj 

Temperature, 

I                               1 

Absolute. 

Fahrenheit. 

Height  H,  Feet. 

520° 

700 

239 

250.9                157.6 

67.8 

Absolute,  or 

800 

339 

172.4                115.8 

55.7 

59°  F. 

1000 

539 

149.1 

100.0 

48.7 

1100 

639 

148.8 

98.9 

48.2 

1200 

739 

152.0 

100.9 

49.1 

1400 

939 

159.9 

105.7 

51.2 

1600 

1139 

168.8 

111.0 

53.5 

2000 

1539 

206.5 

132.2 

63.0 

All  attempts  to  base  a  practical  formula  for  chimneys  upon  the 
theoretical  formulae  of  Peclet  and  Rankine  have  failed  on  account  of 
the  impossibility  of  assigning  correct  values  to  the  so-called  "con- 
stants" G  and/.  (See  Trans.  A.  S.  M.  E.,  xi.  984.) 

Force  or  Intensity  of  Draft. — The  force  of  the  draft  is  equal  to 
the  difference  between  the  weight  of  the  column  of  hot  gases  inside 
of  the  chimney  and  the  weight  of  a  column  of  the  external  air  of  the 
same  height.  It  is  measured  by  a  draft-gauge,  usually  a  U  tube 
partly  filled  with  water,  one  leg  connected  by  a  pipe  to  the  interior  of 
the  flue,  and  the  other  open  to  the  external  air.  (See  Fig.  112,  p.  359.) 

If  D  is  the  density  of  the  air  outside,  d  the  density  of  the  hot  gas 
inside,  in  Ibs.  per  cu.  ft.,  U  the  height  of  the  chimney  in  feet,  and  0.192 
the  factor  for  converting  pressure  in  Ibs.  per  sq.  ft.  into  inches  of 
water-column,  then  the  formula  for  the  force  of  draft  expressed  in 
inches  of  water  is, 

F—  O.W'2h(D  —  d). 

The  density  varies  with  the  absolute  temperature  (see  Rankine). 

d  =  -T—O.OS±:     D  —  0.0807— , 
r>  T* 

where  TO  is  the  absolute  temperature  at  32°  F.,  =  493,  r1  the  absolute 
temperature  of  the  chimney-gases,  and  r,2  that  of  the  external  air. 
Substituting  these  values  the  formula  for  force  of  draft  becomes 


7.64 


J.95 


To  find  the  maximum  intensity  of  draft  for  any  given  chimney, 
the  heated  column  being  600°  F.,  and  the  external  air  GO0,  multiply 
the  height  above  grate  in  feet  by  .0073,  and  the  product  is  the  draft 
in  inches  of  water. 


sure  of  draft,  as  measured  by  a  draft-gauge.  It  here  means  maximum  quantity 
or  weight  of  gases  passed  up  the  chimney.  The  maximum  intensity  is  found 
only  with  maximum  temperature,  but  after  the  temperature  reaches  about  622°  V. 
the  density  of  the  gas  decreases  more  rapidly  than  its  velocity  increases,  so  that 
the  weight  is  a  maximum  about  622°  F.,  as  shown  by  Rankine. 


424 


STEAM-BOILER  ECONOMY. 


HEIGHT    OF   WATER-COLUMN     DUE     TO    UNBALANCED   PRESSURE   IN    CHIMNEY    100 

FEET  HIGH.     (The  Locomotive,  1884.) 


£      >> 

H      O 

Temperature  of  the  External  Air—  Barometer,  14.7  Ibs.  per  Square  Inch. 

0° 

10° 

20° 

30° 

40° 

50° 

60° 

TO0 

80° 

90° 

100° 

200 

.453 

.419 

.384 

.353 

.321 

.292 

.263 

.234 

.209 

.182 

.157 

220 

.488 

.453 

.419 

.388 

.355 

.326 

.298 

.269 

.244 

.217 

.192 

240 

.520 

.488 

.451 

.421 

.388 

.359 

.330 

.301 

.276 

.250 

.225 

260 

.r>55 

.528 

.484 

.453 

.420 

.392 

.363 

.334 

.309 

.282 

.257 

280 

.584 

.549 

.515 

.482 

.451 

.422 

.394 

.365 

.340 

.313 

.^88 

300 

.611 

.576 

.541 

.511 

.478 

.449 

.420 

.392 

.367 

.340 

1315 

320 

.637 

.603 

.568 

.538 

.505 

.476 

.447 

.419 

.394 

.367 

.342 

340 

.662 

.638 

.593 

.563 

.530 

.501 

.472 

.443 

.419 

.392 

.367 

360 

.687 

.653 

.618 

.588 

.555 

.526 

.497 

.468 

.444 

.417 

.392 

380 

.710 

.676 

.641 

.611 

.578 

.549 

.520 

.492 

.467 

.440 

.415 

400 

.732 

.697 

.662 

.632 

.598 

.570 

.541 

.513 

.488 

.461 

.436 

420 

.754 

.718 

.684 

.653 

.620 

.591 

.563 

.534 

.509 

.482 

.457 

440 

.773 

.739 

.705 

.674 

.641 

.612 

.584 

.555 

.530 

.503 

.478 

460 

.793 

.758 

.724 

.694 

.660 

.632 

.603 

.574 

.549 

.522 

.497 

480 

.810 

.776 

.741 

.710 

.678 

.649 

.620 

.591 

.566 

.540 

.515 

500 

.829 

.791 

.760 

.730 

.697 

.669 

.639 

.610 

.586 

.559 

.534 

For  any  other  height  of  chimney  than  100  ft.  the  height  of  water- 
column  is  found  by  simple  proportion,  the  height  of  water-column 
being  directly  proportional  to  the  height  of  chimney. 

The  calculations  have  been  made  for  a  chimney  100  ft.  high,  with 
various  temperatures  outside  and  inside  of  the  flue,  and  on  the  sup- 
position that  the  temperature  of  the  chimney  is  uniform  from  top  to 
bottom.  This  is  the  basis  on  which  all  calculations  respecting  the 
draft-power  of  chimneys  have  been  made  by  Rankine  and  other 
writers,  but  it  is  very  far  from  the  truth  in  most  cases.  The  differ- 
ence will  be  shown  by  comparing  the  reading  of  the  draft-gauge  with 
the  table  given.  In  one  case  a  chimney  122  ft.  high  showed  a  tem- 
perature at  the  base  of  320°,  and  at  the  top  of  230°." 

Box,  in  his  "  Treatise  on  Heat/'  gives  the  following  table : 

DRAFT    POWERS    OF    CHIMNEYS,    ETC.,  WITH    THE   INTERNAL    AIR    AT    552°     AND 
THE   EXTERNAL   AIR    AT   62°,    AND   WITH   THE   DAMPER   NEARLY   CLOSED. 


^a 

Theoretical  Velocity 

^e 

r/ 

Theoretical  Velocity 

°  ^ 

.S  •-" 

in  Feet  per  Second. 

.2  **> 

.5  c 

in  Feet  per  Second. 

£  a  aj 

=  2 

•^  B« 

si 

fag 

£  u> 

•SPSS 

£'c> 

*•  &-C 

Cold  Air 

'Hot  Air 

W-S 

i  K 

Cold  Air 

Hot  Air 

0 

ft£° 

Entering. 

at  Exit. 

Q  o  ° 

C-, 

Entering. 

at  Exit. 

10 

.073 

17.8 

35.6 

80 

.585 

50.6 

101.2 

20 

.146 

25.3 

50.6 

90 

.657 

53.7 

107.4 

30 

.219 

31.0 

62.0 

100 

.730 

56.5 

113.0 

40 

.292 

35.7 

71.4 

120 

.876 

62.0 

124.0 

50 

.365 

40.0 

80.0 

150 

1.095 

693 

138.6 

60 

.438 

43.8 

87.6 

175 

1.277 

74.3 

149.6 

70 

.511 

47.3 

94.6 

200 

1.460 

80.0 

160.0 

CHIMNEYS. 


425 


Rate  of  Combustion  Due  to  Height  of  Chimney. — Trowbridge's 
"Heat  and  Heat-engines"  gives  the  following  table  showing  the 
heights  of  chimney  for  producing  certain  rates  of  combustion  per 
sq.  ft.  of  section  of  the  chimney.  It  may  be  approximately  true  for 


Lbs.  of  Coal 

Lbs.  of  Coal 

Lbs.  of  Coal 

Burned  per 

Lbs.  of  Coal 

Burned  per 

Heights 

Burned  per 
Hour  per 

Square  Foot 
«'f  Grate,  the 

Heights 

Burned  pel- 
Hour  per 

Square  Foot 
of  Grate,  the 

in 
Feet. 

Square  Foot 
of  Section 

Ratio  of  Grate 
to  Section  of 

in 
Feet. 

Square  Foot 
of  Section 

Ratio  of  Grate 
to  Section  of 

of  Chimney. 

Chimney 
being  8  to  1 

of  Chimney. 

Chimney 
being  8  to  I. 

20 

60 

7  5 

70 

126 

15.8 

25 

68 

8.5 

75 

131 

16.4 

30 

76 

9.5 

80 

135 

16.9 

35 

84 

10.5 

85 

139 

17.4 

40 

93 

11.6 

90 

144 

18.0 

45 

99 

12.4 

95 

148 

18.5 

50 

105 

13.1 

100 

152 

19.0 

55 

111 

13.8 

105 

156 

19.5 

60 

116 

14.5 

110 

160 

20.0 

65 

121 

15.1 

anthracite  in  moderate  and  large  sizes,  but  greater  heights  than  are 
given  in  the  table  are  needed  to  secure  the  given  rates  of  combustion 
with  small  sizes  of  anthracite,  and  for  bituminous  coal  smaller  heights 
will  suffice  if  the  coal  is  reasonably  free  from  ash — 5  per  cent  or  less. 
Thurston's  rule  for  rate  of  combustion  effected  by  a  given  height 
of  chimney  (Trans.  A.  S.  M.  E.,  xi.  991)  is:  Subtract  1  from  twice 
the  square  root  of  the  height  and  the  result  is  the  rate  of  combustion 
in  pounds  per  square  foot  of  grate  per  hour,  for  anthracite.  Or  rate 
—  2  I//J  _  i?  in  which  h  is  the  height  in  feet.  This  rule  gives  the  fol- 
lowing : 

h=    50        60         70         80         90     100     110       125       150       175       200 
21^-1  =  13.14    14.49    15.73    16.89    17.97    19    19.97    21.36    23.49    25.45    27.28 

The  results  agree  closely  with  Trowbridge's  table  given  above.  In 
practice  the  high  rates  of  combustion  for  high  chimneys  given  by  the 
formula  are  not  generally  obtained  for  the  reason  that  with  high 
chimneys  there  are  usually  long  horizontal  flues  serving  many  boilers, 
and  the  friction  and  the  interference  of  currents  from  the  several 
boilers  are  apt  to  cause  the  intensity  of  draft  in  the  branch  flues  lead- 
ing to  each  boiler  to  be  much  less  than  that  at  the  base  of  the 
chimney.  The  draft  of  each  boiler  is  also  usually  restricted  by  a 
damper  and  by  bends  in  the  gas-passages.  In  a  battery  of  several 
boilers  connected  to  a  chimney  150  ft.  high,  the  author  found  a  draft 
of  f-in.  water-column  at  the  boiler  nearest  the  chimney,  and  only 
I -in.  at  the  boiler  farthest  away.  The  first  boiler  was  wasting  fuel 
fro  ni  too  high  temperature  of  the  chimney-gases,  900°,  having  too 
liirge  a  grate-surface  for  the  draft,  and  the  last  boiler  was  working 
below  its  rated  capacity  and  with  poor  economy,  on  account  of  insuffi- 
cient draft. 


426 


STEAM-BOILER  ECONOMY. 


The  effect  of  changing  the  length  of  the  flue  leading  into  a 
chimney  60  ft.  high  and  2  ft.  9  ins.  square  is  given  in  the  following 
table,  from  Box  on  "  Heat  " : 


Length  of  Flue  in  Feet. 

Horse-power. 

Length  of  Flue  in  Feet. 

Horse-power. 

50 

107.6 

800 

56.1 

100 

100.0 

1.000 

51.4 

200 

85.3 

1.500 

43.3 

400 

70.8 

2.000 

38.2 

600 

62.5 

3.000 

31.7 

The  temperature  of  the  gases  in  this  chimney  was  assumed  to  be 
552°  F.,  and  that  of  the  atmosphere  62°. 

High  Chimneys  not  Necessary. — Chimneys  above  150  ft.  in  height 
are  very  costly,  and  their  increased  cost  is  rarely  justified  by  increased 
efficiency.  In  recent  practice  it  has  become  somewhat  common  to 
build  two  or  more  smaller  chimneys  instead  of  one  large  one.  A 
notable  example  is  the  Spreckels  Sugar  Refinery  in  Philadelphia, 
where  three  separate  chimneys  are  used  for  one  boiler-plant  of  7500 
H.P.  The  three  chimneys  are  said  to  have  cost  several  thousand 
dollars  less  than  a  single  chimney  of  their  combined  capacity  would 
have  cost.  Very  tall  chimneys  have  been  characterized  by  one  writer 
as  "  monuments  to  the  folly  of  their  builders." 

Height  of  Chimney  required  for  Different  Fuels. — The  minimum 
height  necessary  varies  with  the  fuel,  wood  requiring  the  least,  then 
.good  bituminous  coal,  and  fine  sizes  of  anthracite  the  greatest.  It 
also  varies  with  the  character  of  the  boiler — the  smaller  and  more 
circuitous  the  gas-passages  the  higher  the  stack  required;  also  with 
the  number  of  boilers,  a  single  boiler  requiring  less  height  than  several 
that  discharge  into  a  horizontal  flue.  No  general  rule  can  be  given. 

Size  of  Chimneys  corresponding  to  Given  Capacity  of  Boilers.— 
The  formula  given  below,  and  the  table  calculated  therefrom  for 
chimneys  up  to  96  ins.  diameter  and  200  ft.  high  were  first  published 
by  the  author  in  1884  (Trans.  A.  S.  M.  E.,  vi.  81).  They  have  met 
with  much  approval  since  'that  date  by  engineers  who  have  used 
them,  and  have  been  frequently  published  in  boiler-makers*  catalogues 
and  elsewhere.  The  table  is  now  extended  to  cover  chimneys  up  to 
12  ft.  diameter  and  300  ft.  high.  The  sizes  corresponding  to  the 
given  commercial  horse-powers  are  believed  to  be  ample  for  all  cases 
in  which  the  draft  areas  through  the  boiler~flues  and  connections  are 
sufficient,  say  not  less  than  20  per  cent  greater  than  the  area  of  the 
chimney,  and  in  which  the  draft  between  the  boilers  and  chimney  is 
not  checked  by  long  horizontal  passages  and  right-angled  bends. 

Note  that  the  figures  in  the  table  correspond  to  a  coal  consumption 
of  5  Ibs.  of  coal  per  liorse-power  per  hour.  This  liberal  allowance  is 
made  to  cover  the  contingencies  of  poor  coal  being  used,  and  of  the 
boilers  being  driven  beyond  their  rated  capacity.  In  large  plants, 


CHIMNEYS.  427 

-with  economical  boilers  and  engines,  good  fuel  and  other  favorable 
conditions,  which  will  reduce  the  maximum  rate  of  coal  consumption 
at  any  one  time  to  less  than  5  Ibs.  per  H.P.  per  hour,  the  figures  in 
the  table  may  be  multiplied  by  the  ratio  of  5  to  the  maximum 
expected  coal  consumption  per  H.P.  per  hour.  Thus,  with  conditions 
which  make  the  maximum  coal  consumption  only  2.5  Ibs.  per  hour, 
the  chimney  300  ft.  high  x  12  ft.  diameter  should  be  sufficient  for 
6155  X  2  =  12,310  horse-power.  The  formula  is  based  on  the  follow- 
ing data: 

1.  The  draft-power  of  the  chimney  varies  as  the  square  root  of  the 
height. 

2.  The  retarding  of  the  ascending  gases  by  friction  may  be  con- 
sidered as  equivalent  to  a  diminution  of  the  area  of  the  chimney,  or 
to  a  lining  of  the  chimney  by  a  layer  of  gas  which  has  no  velocity. 
The  thickness  of  this  lining  is  assumed  to  be  2  ins.  for  all  chimneys, 
or  the  diminution  of  area  equal  to  the  perimeter  x  2  ins.  (neglecting 
the  overlapping  of  the  corners  of  the  lining).     Let  D  =  diameter  in 
feet,  A  =  area,  and  E  =  effective  area  in  square  feet. 

8D 
For  square  chimneys,  E  =  D*  -  •  —  - 

-L/w 

-  ~    =  A  -  0.5914/17 


For  round  chimneys,   E  =  ~ 

4 

For  simplifying  calculations,  the  coefficient  of   VA  may  be  taken 
as  0.6  for  both  square  and  round  chimneys,  and  the  formula  becomes 

E  =  A  —  0.6IXZ 

3.  The  power  varies  directly  as  this  effective  area  E. 

4.  A  chimney  should  be  proportioned  so  as  to  'be  capable  of  giving 
sufficient  draft  to  cause  the  boiler  to  develop  much  more  than  its 
rated  power,  in  case  of  emergencies,  or  to  cause  the  combustion  of 
5  Ibs.  of  fuel  per  rated  horse-power  of  boiler  per  hour. 

5.  The  power  of  the  chimney  varying  directly  as  the  effective  area, 
E,  and  as  the  square  root  of  the  height,  //,  the  formula  for  horse- 
power of  boiler  for  a  given  size  of  chimney  will  take  the  form  H.P. 
=  CE  V39  in  which  C  is  a   constant,  the  average  value  of  which, 
obtained  by  plotting  the  results  obtained  from  numerous  examples  in 
practice,  the  author  finds  to  be  3.33. 

The  formula  for  horse-power  then  is 

H.P.  =  3.33#  VH,     or     H.P.  =  3.33(.l  -  0.6  VA)  VU. 
If  the  horse-power  of  boiler  is  given,  to  find  the  size  of  chimney, 
the  height  being  assumed, 

^n-r, 

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428 


STEAM-BOILER  ECONOMY. 


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CHIMNEYS.  429 

For  round  chimneys,  diameter  of  chimney  =  diam.  of  E  -\-  4  ins. 

For  square  chimneys,  side  of  chimney  =  V  E  -\-  4  ins. 

If  effective  area  E  is  taken  in  square  feet,  the  diameter  in  inches 
is  d  =  13.54  VE  -f-  4  ins.,  and  the  side  of  a  square  chimney  in  inches 
is  s  =  12  VW+  4  ins. 

If  horse-power  is  given  and  area  assumed,  the  height  H  ==• 
0.3H.PA3 


In  proportioning  chimneys  the  height  is  generally  first  assumed, 
with  due  consideration  to  the  heights  of  surrounding  buildings  or 
hills  near  to  the  proposed  chimney,  the  length  of  horizontal  flues,  the 
character  of  coal  to  be  used,  etc.,  and  then  the  diameter  required  for 
the  assumed  height  and  horse-power  is  calculated  by  the  formula  or 
taken  from  the  table. 


CHAPTEE   XVII. 

MISCELLANEOUS. 

ECONOMIZERS. — APPARATUS    FOR    INDICATING    FURNACE    CONDITIONS.— THE 

ARNDT  ECONOMETER.— FLUE-GAS  ANALYSES  AND  THE  HEAT  BALANCE. 

DESIGNING  BOILERS  FOR  A  STREET-RAILWAY  PLANT.— Loss  OF  FUEL  DUE 
TO  KEEPING  UP  STEAM-PRESSURE  IN  IDLE  BOILERS.— COAL  USED  IN 
BANKED  FIRES  NOT  A  MEASURE  OF  RADIATION.— COST  OF  COAL  PER  BOILER 
HORSE-POWER  PER  YEAR. — BOILER-ROOM  LABOR. — STEAM-BOILER  PRACTICE 
OF  THE  FUTURE. 

Economizers. — The  Green  economizer,  Fig.  131,  consists  of  a  rec- 
tangular chamber  of  brickwork  filled  with  a  great  number  of  vertical 
cast-iron  water-tubes.  The  waste  heat  from  the  cylinder  boiler  is 
carried  into  this  chamber  before  being  allowed  to  enter  the  chimney, 
and  heats  the  feed-water,  which  passes  through  the  tubes  under  pressure, 
to  a  temperature  approaching  that  of  the  steam  generated  in  the  boiler. 
This  economizer  is  very  commonly  used  in  England  with  Lancashire 
boilers,  and  has  been  largely  introduced  in  this  country,  especially 
in  large  plants  such  as  sugar  refineries.  The  advisability  of  its  use 
in  any  particular  case  is  a  matter  of  close  calculation,  in  which  the 
factors  are  quantity  of  coal  used  and  of  water  evaporated  by  the  boilers, 
temperature  of  the  feed-water,  temperature  of  the  waste  gases  from  the 
boiler,  cost  of  the  economizer,  annual  cost  for  interest  and  probable 
repairs,  and  probable  saving  by  the  economizer. 

Data  for  Proportioning  a  Green  Economizer. — The  Fuel  Econo- 
mizer Co.  makes  the  following  statement  concerning  the  amount  of 
heating  surface  to  be  provided  in  an  economizer  to  be  used  in  connec- 
tion with  a  given  amount  of  boilers,  and  concerning  the  results  which 
may  be  expected  from  the  economizer : 

We  have  found  in  practice  that  by  allowing  4  sq.  ft.  of  heating 
surface  per  boiler  horse-power  (34^  Ibs.  of  water  evaporated  from  and 
at  212°  =  1  H.P.),  we  are  able  to  raise  the  feed-water  60°  for  every 
100°  reduction  in  the  temperature,  entering  the  economizer  with  gases 
from  450°  to  600°. 

With  temperature  entering  the  economizer  at  600°  to  700°  we  have 
allowed  a  heating  surface  of  4^  to  5  sq.  ft.  of  heating  surface  per 

430 


ECONOMIZERS. 


431 


432  STEAM-BOILER  ECONOMY. 

boiler  horse-power,  and  for  every  100°  reduction  of  gases  we  have 
obtained  about  65°  rise  in  temperature  of  the  water;  the  temperature 
of  the  feed-water  entering  averaging  from  60°  to  120°. 

With  5000  sq.  ft.  of  boiler  heating  surface  (plain  cylinder  boilers) 
developing  1000  H.P.,  we  should  recommend  using  5  sq.  ft.  of 
economizer  heating  surface  per  boiler  H.P.,  or  an  economizer  of  about 
500  tubes,  and  it  should  heat  the  feed-water  about  300°. 

Calcidation  of  the  Saving  Effected  Ijy  an  Economizer. — If  there 
were  no  loss  by  radiation  from  the  economizer,  and  no  leakage  of  air 
into  its  brick  setting,  the  heat  lost  by  the  gases  in  passing  through  it, 
as  measured  by  their  difference  in  temperature  .on  entering  and  leaving, 
would  exactly  equal  the  heat  added  by  the  economizer  to  the  feed- 
water.  The  following  calculation  is  based  on  this  assumption : 

Suppose  the  heating  value  of  1  Ib.  of  fuel  to  be  14,400  B.T.U.; 
that  it  is  thoroughly  burned  with  about  24  Ibs.  of  air,  making  25  Ibs. 
of  gas  per  pound  fuel ;  that  the  boiler  absorbs  70  per  cent  of  the  heat 
generated,  and  the  economizer  40  per  cent  of  the  remainder,  making 
the  efficiency  of  the  boiler  and  economizer  combined  82  per  cent;  and 
the  loss  of  heat  in  the  chimney-gases,  including  radiation  from  the 
boiler,  18  per  cent. 

14  400 
Temperature*  of  the  fire > 25  X  0  24  =  240°° 

Temperature  *  of  gases  leaving  boiler 2400  X  0.30         720° 

*"      "  "       economizer 720x0.60         432° 

B.T.U.          TT.E.t  % 

Heating  value  of  the  fuel  per  Ib 14,400        14.90          100 

Absorbed  by  the  boiler  per  Ib.  fuel 10,080        10.43  70 

Absorbed  by  the  economizer 1,728          1.788          12 

Remainder,  escapes  into  chimney 2,592  2.682  18 

Useful  effect,  boiler  and  economizer. 11,808         12.218          82 

Temperature  of  feed-water  entering  economizer....          62°;  B.T.U.  above  32°     30 

Steam-pressure,  130  Ibs.  gauge;  temperature =355°;        "  "  327 

Total  heat  of  1  Ib.  steam  1190.4  B.T.U. ;  latent  heat,     862  B.T.U. 

Factor  of  evaporation  62°  to  130  Ibs.  —  1.20 

Water  evaporated  per  Ib.  fuel,  12.218  -5-  1.2  =  10.182  Ibs. 

1728  -f-  10.182  =  169.7  B.T.U.  added  to  each  1  Ib.  water  by  the  economizer. 

1 0,080  -5-  10.182  =  990.0    "  "       "     "       "        "        "    "    boiler. 

169.7  +  30  —  199.7  B.T.U.  in  1  Ib.  water  entering  boiler,  =  230°  F 

Of  the  990  B.T.U.  added  to  each  1  Ib.  water  by  the  boiler, 
327  —  199.7  =  127.3  B.T.U.  is  used  in  raising  its  temperature  from 

*  Temperatures  measured  above  the  atmospheric  temperature. 
\  Units  of  Evaporation  =  Ibs.  evaporated  from  and  at  212°. 


ECONOMIZERS.  433 

230°  to  355°,  and  862.7  B.T.TJ.  to  evaporate  it  at  that  temperature. 
The  heat  gained  by  the  economizer  is 

12  169.7 

70     °r     -99^  :  =  17.14  per  cent. 

The  saving  of  fuel  is 

12  169.7 

or  =  14.63  per  cent. 


70  -f  12  1160 

Expressed  in  the  shape  of  a  formula : 

Heat  added  to  each  Ib.  of  water  by  the  economizer 

Saving  of  fuel  =  —  - . 

Heat  added  to  each  Ib.  ot  water  by  both  boiler  and  economizer 

The  above  is  the  usual  method  of  calculating  the  saving  of  fuel 
due  to  the  use  of  an  economizer.  It  is  a  correct  method  when  the 
problem  to  be  solved  is  like  the  following :  "  What  will  the  fuel  saving 
be  when  a  plant  is  provided  with  both  boiler  and  economizer,  giving 
a  combined  efficiency  of  82  per  cent,  as  compared  with  a  plant  pro- 
vided with  boilers  alone,  giving  an  efficiency  of  70  per  cent  ?  " 

It  is  incorrect,  however,  when  the  problem  is  of  a  different  nature, 
such  as  the  following :  "  A  plant  has  boilers  and  economizers  running 
as  in  the  above  example,  the  boiler  utilizing  70  per  cent  and  the 
economizer  12  per  cent  of  the  heating  value  of  the  fuel;  what  is  the 
saving  of  fuel  by  the  use  of  the  economizer  as  compared  with  the  fuel 
that  would  be  used  by  the  same  boilers  delivering  the  same  amount 
of  steam  without  the  economizer  ?  " 

In  this  case  it  is  evident  that  the  boilers  will  be  driven  harder  if 
they  have  to  do  the  work  of  the  economizer  in  addition  to  their  own; 
more  coal  will  be  burned,  the  gases  will  escape  at  a  higher  tempera- 
ture, and  the  efficiency  of  the  boiler  will  be  lower.  It  is  necessary  in 
this  case  to  know  the  rate  at  which  the  efficiency  of  the  boiler 
decreases  with  increased  rate  of  driving,  or  the  "  efficiency  curve  "  of 
the  boiler.  From  the  data  in  the  above  example,  we  may  make  an 
approximate  estimate  of  the  rate  of  decrease  of  efficiency,  using  a 
formula  given  in  the  chapter  on  "  Efficiency  of  Heating  Surface," 
neglecting  the  loss  by  radiation,  as  unimportant. 

W 

The  formula  is  Eaf  =  BEP  —  A-^-9  in   which   E^  —  evaporation 

per  pound  of  fuel  from  and  at  212°;  Ep  —  possible  evaporation  = 
heating  value  of  the  fuel  -~  965.7;  W  =  water  evaporated  per  hour; 
8  =  square  feet  of  heating  surface;  B  =  (T  {  —  t)  -j-  T ^  T}  —  tem- 
perature of  the  fire  and  /  the  temperature  of  the  water  and  steam  in 


434  STEAM-BOILER  ECONOMY. 

the  boiler,  both  being  measured  above  the  atmospheric  temperature; 
A  =  acf  -T-  ( Tl  —  t)7  a  being  the  coefficient  of  efficiency  of  the  heat- 
ing surface,  c  the  specific  heat  of  the  gases,  and  /  the  weight  of  gas 
per  pound  fuel.  For  the  example  given  we  nave:  E*  =  10.43; 
^=14.90;  3^  =  2400;  *  =  293;  #  =  0.88;  /=25;  c  =  0.24; 

W 

a  =  200,  for  good  boiler  practice;    A  =  0.57;    EJ  =  BEP  —  A-=-', 

W  W 

10.43  =  0.88  X  14.90  —  0.57-^;  whence  ™  =  4.7  Ibs.  water  evap- 

o  o 

orated  from  and  at  212°  per  sq.  ft.  of  heating  surface  per  hour.  This 
is  the  rate  of  "  equivalent  evaporation  "  of  the  boiler  when  it  has  the 
economizer  attached,  and  is  utilizing  70  per  cent  of  the  heating-value 
of  the  fuel.  Suppose  now  the  economizer  is  disconnected  and  the 
boiler  is  required  to  do  the  whole  work.  Its  equivalent  evaporation 
must  then  be  increased  in  the  ratio  of  82  to  70,  or  to  4.7  X  82-4-  70 

W 
=  5.51  Ibs.     Substituting  this  value  of  -^-  in  the  formula  we  have 

Ea  =  14.90  X  0.88  -  0.57  X  5.51  =  9.97  Ibs.,  and  the  efficiency 
Ea  ~  Ep  =  9.97  -4-  14.90  =  66.9  per  cent  instead  of  70  per  cent 
obtained  by  the  boiler  when  it  was  run  with  the  economizer. 

The  saving  by  the  use  of  the  economizer  in  this  case  is  - 

o/c 

=  18.41  per  cent,  instead  of  14.63  per  cent,  the  result  obtained  in  the 
first  example. 

Apparatus  for  Indicating  Furnace  Conditions. — It  has  been  shown 
in  Chapter  IX  that  the  efficiency  of  a  steam-boiler  depends  largely 
upon  the  air-supply,  or  in  other  words  upon  the  number  of  pounds 
of  gases  of  combustion  per  pound  of  carbon.  It  is  found  by  experi- 
ment that  the  highest  efficiencies  are  obtained  when  the  weight  of 
gas  is  from  19  to  20  Ibs.  per  pound  of  carbon.  This  corresponds 
approximately  to  a  gas  containing  about  15  per  cent  C02,  5  per  cent  0,. 
80  per  cent  N,  and  no  CO.  A  smaller  air-supply,  giving  fewer  pounds 
of  gas  per  pound  of  carbon,  will  not  be  sufficient  to  maintain  complete 
combustion,  and  will  cause  more  or  less  CO  to  be  in  the  gas.  A 
greater  air-supply,  increasing  the  weight  of  gas  per  pound  of  carbon, 
means  a  greater  loss  of  heat  in  the  chimney-gases,  which  will  then  be 
high  in  0  and  low  in  C02.  As  has  already  been  stated  it  is  a  matter 
of  the  utmost  difficulty,  with  ordinary  firing,  to  regulate  the  air-sup- 
ply so  -as  to  maintain  the  gas  at  the  proper  composition. 

Maximum  economy,  as  far  as  the  operation  of  the  furnace  is  con- 


THE  ARNDT  ECONOMETER. 


435 


cerned,  is  coincident  with  maximum  furnace  temperature,  also  with 
the  gases  of  combustion  containing  from  14  to  10  per  cent  C02  and 
from  5  to  7  per  cent  0.  If  there  could  be  a  continuous  record  con- 
veniently made  either  of  the  furnace  temperature.,  or  of  the  percentage 
of  C02  or  of  0  in  the  gases,  so  that  the  fireman  could  observe  this  record 
and  know  the  condition  of  his  furnace  as  easily  aiid  as  accurately  as 
he  knows  the  steam-pressure  by  consulting  his  steam-gauge,  the  aver- 
age boiler  efficiency  in  ordinary  practice  might  be  raised  10  or  20  per 
cent,  and  a  great  saving  of  fuel  thereby  be  made. 

For  measuring  furnace  temperatures  there  are  now  available  the 
La  Chatelier  electrical  pyrometer,  the  Uehling  &  Steinbart  pneu- 
matic pyrometer,  and  the  Bristol  air-thermometer.* 

For  continuously  indicating  the  percentage  of  C02  in  the  gases 


From  Boiler  Flue 

i p?=- 

FIG.  132. — THE  ARNDT  ECONOMETER. 

there  are  the  Uehling  &  Steinbart  gas  composimeter  and  the  Arndt 
econometer,  a  recent  German  invention.!  A  brief 'description  of  this 
instrument  is  given  below,  and  it  is  illustrated  in  Fig.  132. 

*  For  further  information  concerning  these  instruments  consult  the  circulars 
of  the  manufacturers.  The  American  agent  of  the  electrical  pyrometer  is  Chas.' 
Engelhard,  41  Cortlandt  Street,  New  York.  Uehling  &  Steinbart's  address  is 
Carlstadt,  N.  J.,  and  the  Bristol  Mfg/Co.'s  is  Waterbury,  Conn. 

f  Joseph  Wilckes,  Agent,  106  Fulton  Street,  New  York. 


436  STEAM-BOILER  ECONOMY. 

The  Arndt  Econometer.  —  This  apparatus  consists  essentially  of  a 
delicate  balance  which  continually  weighs  the  flue-gases,  and  thus 
indicates  their  composition.  Carbonic  acid  gas  is  52  per  cent  heavier 
than  air;  the  weight  of  the  flue-gases  thus  depends  upon  the  amount 
of  carbonic  acid  gas  they  contain,  and  the  weight  is  an  index  of  the 
composition.  The  gas  is  drawn  from  the  furnace-flue  through  a 
small-sized  pipe  and  passes  first  through  two  gas-filters,  a  coarse  and 
a  fine.  The  purpose  of  these  filters  is  to  remove  the  dust,  which, 
if  allowed  'to  pass  on,  would  accumulate  in  the  weighing  apparatus 
and  vitiate  the  results.  The  first  filter  is  placed  as  near  as  may  be  to 
the  boiler,  in  order  to  prevent  the  dust  passing  on  and  obstructing  the 
pipes.  After  passing  the  second  filter,  the  gas  passes  through  a  drier 
which  is  filled  with  calcium  chloride  to  absorb  the  moisture.  Passing 
from  the  drier  through  the  connecting-pipes,  the  gas  is  finally  dis- 
charged through  a  rose-head  into  the  gas-holder,  which  is  a  balloon- 
shaped  vessel  of  glass,  its  open  mouth  hanging  within  the  glass  cup. 
From  the  cup  the  gas  is  drawn  through  the  connecting-pipe  which 
connects  with  the  chimney,  through  an  aspirator  if  necessary.  There 
is  thus  a  constant  circulation  of  gas  through  the  instrument,  and  the 
gas-holder  is  constantly  filled  with  gas  representing  the  product  of 
the  furnace.  The  gas-holder,  as  will  be  seen,  is  hung  from  one  end 
of  a  delicate  balance,  whose  pointer  moves  over  a  scale  which  is  gradu- 
ated so  as  to  indicate  directly  the  percentage  of  carbonic  acid.  The 
scale  is  mounted  in  a  cast-iron  box  with  a  glass  front  which  is  air- 
tight except  for  a  small  air-inlet.  It  is  essential  that  the  box  be  filled 
with  atmospheric  air,  and  the  regulating  cocks  are  so  adjusted  that 
the  draft  through  the  tube  constantly  draws  the  air  from  the  case,  and 
so  insures  that  it  shall  be  filled  with  air  only. 

A  suitable  supply  of  air  gives  from  12  to  15  per  cent  of  carbonic 
acid  in  the  flue-gas,  and  any  deficiency  in  that  percentage  indicates 
that  too  much  air  is  being  admitted. 

Flue-gas  Analyses  and  the  Heat-balance.  —  In  the  heat-balance 
computed  from  the  results  of  a  boiler-test  —  see  Chapter  XIV,  pages  342 
and  359  —  the  heat  which  is  "unaccounted  for"  sometimes  amounts  to 
quite  a  large  percentage  of  the  total  heating  value  of  the  coal.  In  one 
case,  with  soft  coal  very  high  in  moisture,  the  author  found  it  to  be 
more  than  20  per  cent,  even  after  a  liberal  allowance  had  been  made 
for  radiation.  Some  probable  causes  of  this  shortage  in  the  heat- 
balance  are  the  following  : 

1.  The  calculations  of  heat  lost  in  the  chimney-gas  are  based  on 
the  supposition  that  the  dry  gas  contains  only  C02,  CO,  0,  and  !N". 
The  fact  is  that  for  a  short  period  after  each  firing  of  fresh  coal  the 
gas  may  also  contain  H,  formed  by  decomposing  the  moisture  in  the 
coal,  and  CH4,  distilled  from  the  coal,  which  are  not  burned  because 
the  furnace  conditions  were  unfavorable.  The  gas  may  also  contain 
some  S02  and  N02>  from  the  sulphur  and  the  nitrogen  in  the  coal. 
As  much  as  1.37  per  cent  of  N0?  has  been  found  in  chimney  -gases 
by  Dr.  A.  II.  Gill.*  This  would  indicate  the  possibility  that  a  small 


*  Engineering  Wewa,  Feb.  18,  1897,  p.  107. 


DESIGNING  BOILERS  FOR  STREET-RAILWAY  PLANT.    437 


quantity  of  oxides  of  nitrogen  may  be  produced  from  the  nitrogen 
of  the  air  in  the  boiler-furnace. 

2.  The  gas  analyzed  may  not  be  a  fair  average  sample  of  the  gas 
in  the  flue.     The  constitution  of  gas  produced  in  an  ordinary  furnace 
is  constantly  varying;  within  a  space  of  ten  minutes  it  may  vary  from 
low  C02,  high  CO,  and  no  0,  through  high  C02,  no  CO,  and  low  0,  to 
low  C02,  no  CO,  and  high  0.     The  gas  is  also  apt  to  vary  in  composi- 
tion in  different  parts  of  the  flue.     See  "  Sampling  Flue-gases,"  page 
365. 

3.  The  analysis  for  C02,  CO,  0,  and  N  (by  difference)  may  be 
erroneous.     Sometimes  analyses  are  published  which  show  the  total 
of  C02,  CO,  and  0  to  be  only  about  16  per  cent.     It  is  very  improb- 
able that  the  sum  of  these  gases  can  ever  be  as  low  as  16  per  cent  in 
boiler  practice,  except  possibly  for  a  minute  or  so  after  firing  fresh 
coal,  when  large  volumes  of  H  and  of  CH4  may  be  given  off.     When 
carbon  is  thoroughly  burned  to  C02,  either  with  or  without  excess  of 
air,  the  sum  of  C02  and  0  should  equal  20.9  per  cent,  and  the  N  79.1 
of  the  volume  of  the  gases.     Carbon  burned  to  CO  only,  without 
excess  of  air  would  give  a  gas  containing  34.5  per  cent  CO  and  65.5 
per  cent  N.     Hydrogen  burned  in  air  without  excess  would  give  a 
dry  gas  of  100  per  cent  N.     The  normal  value  of  the  sum  of  C02  and 
0  being  20.9  per  cent,  and  the  production  of  CO  by  imperfect  com- 
bustion tending  to  make  the  sum  of  C02,  CO,  and  0  higher  than  this 
figure,   it   would   require    the   burning   of    a    large    percentage    of 
hydrogen,  or  the  dilution  of  the  gas  by  a  large  volume  of  hydrocar- 
bons, to  reduce  the  sum  of  C02,  CO,  and  0  to  as  low  a  figure  as  16. 
If  the  sum  is  below  19,  an  error  in  the  analysis  may  be  suspected. 

Designing  Boilers  for  a  Small  Street-railway  Plant,* — In  entering 
upon  the  studies  preliminary  to 
the  design  of  the  steam-boilers 
for  a  sm^ll  or  medium-sized 
electrical  street-railway  power- 
plant  the  engineer  must  take 
into  consideration  some  pe- 
culiar features  of  the  service  re- 
quired from  the  boilers  which 
differ  more  or  less  from  those 
which  govern  the  design  of 
boilers  for  other  purposes,  such 
as  a  factory.  Such  features 
are :  the  extreme  variations  of 
the  load  upon  the  engines  from 
hour  to  hour,  and  the  conse- 
quent variation  in  the  quantity 
of  steam  to  be  furnished;  the 
prime  necessity  of  having  the 
boiler-plant  constantly  in  con- 


10      12 

Noon 


FIG.  133. — LOAD-DIAGRAM  OF  A  STREET- 
KAILWAY  PLANT. 


dition  to  furnish  the  maximum  amount  of  steam  required  during  the 
*  From  an  article  by  the  author  in  Street  Railway  Review,  February,  1899. 


438  STEAM-BOILER  ECONOMY. 

hours  of  heaviest  load;  the  absence  of  holidays  or  slack  seasons  during 
which  general  repairs  or  alterations  may  be  made;  and  the  consider- 
able uncertainty  that  exists  before  the  plant  is  put  in  operation  con- 
cerning the  actual  amount  of  power  that  may  be  required  and  the 
probable  additions  that  may  be  needed  as  the  road  is  extended  or  as 
traffic  increases.  The  first  considerations,  therefore,  in  the  design  of 
the  boiler-plant  are  certainty  of  operation  under  the  severest  load,  and 
capacity  for  furnishing  the  maximum  amount  of  steam  that  may  be 
needed  under  the  most  adverse  conditions,  such  as  a  combination  of 
heaviest  load,  bad  weather,  poor  coal,  and  a  portion  of  the  boiler-plant 
being  laid  off  for  cleaning  or  repairs. 

To  meet  these  requirements  it  is  necessary  not  only  to  have  the 
boilers  of  sufficient  capacity  to  meet  the  greatest  demand  for  steam, 
but  also  to  have  enough  boilers  to  allow  one  of  them  to  be  laid  off 
without  curtailing  the  steam-supply  below  the  maximum  quantity 
that  may  at  any  time  be  required  by  the  engines.  In  even  the 
smallest-sized  plant  it  is  advisable  to  have  not  less  than  three  boilers, 
any  two  of  which  are  able  to  run  the  plant  at  the  time  of  heaviest 
loading.  In  larger  plants,  four,  five,  or  more  boilers  may  be  installed, 
and  arranged  that  any  one  of  them  may  be  laid  off  at  any  time  for 
cleaning  or  repairs  without  interfering  with  the  operation  of  the 
others. 

Assuming  that  the  boiler-plant  is  to  contain  one  boiler  more  than 
is  sufficient  to  generate  the  steam  required  under  the  conditions  of 
maximum  load,  the  poorest  coal  being  supplied  that  is  ever  expected 
to  be  used  at  the  station,  and  the  weather  the  most  unfavorable  as 
regards  the  draft  and  the  amount  of  moisture  in  the  air  and  in  the 
coal,  we  proceed  to  consider  the  number,  size,  proportions,  and  style 
of  the  boilers  to  be  selected. 

The  boiler-plant  is  usually  one  of  the  last  of  the  divisions  of  the 
complete  power-plant  that  are  to  be  designed.  Before  designing  it 
we  must  know  the  maximum  quantity  of  steam  that  will  be  needed. 
The  electrical  engineer  of  the  railway  company  will  furnish  data  as 
to  the  electrical  horse-power  that  will  be  required  from  the  dynamos, 
and  he  will  hand  to  the  steam  engineer  a  diagram  something  like  the 
one  shown  in  the  accompanying  cut,  Fig.  133,  giving  the  heaviest 
loads  expected  on  the  dynamos  during  twenty-four  hours.  From 
these  data  the  steam-engines  will  be  selected  or  designed,  involving  a 
long  study  of  the  relative  advantages  and  disadvantages  of  horizontal 
and  vertical,  of  simple  and  compound,  of  condensing  and  non-con- 
densing engines,  of  their  size  and  of  their  probable  steam-consumption 
at  different  loads.  The  two  "peaks"  of  the  load-diagram  will  be 
carefully  considered,  and  the  question  will  be  decided  whether  these 
peaks  are  to  be  taken  care  of  by  storage-batteries,  by  overloading  the 
engines  or  dynamos,  or  by  the  use  of  a  separate  engine  and  dynamo 
to  be  operated  during  three  or  four  hours  of  the  day  when  the  load 
is  heaviest. 

The  steam-engine  questions  being  decided,  a  careful  calculation  is 


DESIGNING  BOILERS  FOR  STREET-RAILWAY  PLANT.    439 

then  made  of  the  probable  steam  consumption  per  hour  during  the 
single  hour  or  fraction  of  an  hour  of  maximum  load,  having  due  con- 
sideration for  the  fact  that  an  overloaded  engine  may  be  very  wasteful 
of  steam.  How  wasteful  will  depend  on  the  type  of  engine.  Not 
until  this  question  is  settled  is  it  time  to  prepare  the  design  of  the 
boiler-plant. 

The  boilers,  after  one  of  them  is  reserved  for  cleaning  or  repairs, 
must  be  capable  of  furnishing  sufficient  steam  to  the  engines  during  the 
time  of  the  peak  of  the  load,  even  when  the  coal  is  poor  and  the  weather 
bad,  and  the  engine  not  in  its  best  condition  as  to  steam-tightness 
and  valve-adjustment ;  and  to  this  consideration  every  other  one.  such 
as  first  cost  of  boilers,  or  economy  of  coal,  must  be  made  secondary. 

The  maximum  number  of  pounds  of  steam  per  hour  now  being 
given,  and  the  pressure  of  steam  required  by  the  engines  and  the 
probable  feed-water  temperature  being  known,  we  have  the  data  with 
which  to  begin  figuring  on  the  boilers.  By  referring  to  a  table  of 
"  factors  of  evaporation,"  we  may  reduce  this  number  to  the  equivalent 
number  of  pounds  per  hour  evaporated  "from  and  at  212°  F." 
Dividing  this  by  34^  gives  the  number  of  "  boiler  horse-power."  A 
slight  allowance,  say  1  per  cent,  may  be  added  to  cover  loss  of  heat 
due  to  radiation  from  the  steam-pipes. 

Having  the  amount  of  work  to  be  done  by  the  boilers  during  the 
time  of  the  peak  of  the  load,  we  now  consider  how  this  capacity  is  to 
be  obtained.  The  first  essential  in  a  boiler  is  its  capacity  to  burn 
coal.  No  matter  what  its  type  or  proportions,  or  the  extent  of  its 
heating  surface,  it  will  not  develop  the  required  power  unless  it  can 
burn  enough  coal.  This  qualification  strictly  does  not  belong  to  the 
boiler  itself,  but  chiefly  to  the  furnace  under  the  boiler,  and  largely 
to  the  chimney,  to  the  area  of  flues  or  gas-passages  through  or  beyond 
the  boiler,  and  to  the  quality  of  the  coal.  We  must  therefore  propor- 
tion ^he  furnace  before  we  proportion  the  boiler,  and  to  do  this  we 
must  first  find  out  how  many  pounds  of  coal  are  to  be  burned  per 
hour  during  the  time  of  maximum  steam  demand.  This  is  rather  j» 
complex  question,  for  it  involves  many  variable  elements,  such  as  the 
quality  of  the  coal,  the  kind  of  furnace,  the  rate  of  driving  of  the 
boiler,  and  the  skill  of  the  fireman. 

The  number  of  pounds  of  coal  required  per  hour  will  be  equal  to 
the  quotient  obtained  by  dividing  the  equivalent  evaporation  from 
and  at  212°  per  hour,  in  pounds  by  the  number  of  pounds  of  water 
that  may  be  evaporated  from  and  at  212°  by  1  Ib.  of  coal.  This  latter 
number  will  vary  anywhere  from  12,  when  the  best  grade  of  semi- 
bituminous  coal,  low  in  ash,  is  used,  in  a  furnace  adapted  to  burn  all 
the  volatile  part  of  the  coal,  with  a  boiler  so  proportioned  as  to  be 
capable  of  absorbing  75  per  cent  of  the  heat  generated  in  the  furnace, 
and  with  skilful  firing,  down  to  5  Ibs.  or  less,  with  a  poor  grade  of 
western  bituminous  coal,  high  in  moisture,  ash,  and  sulphur,  burned 
in  an  ordinary  furnace  directly  under  the  boiler,  with  no  provision 
for  burning  the  volatile  matter  or  preventing  smoke,  with  a  boiler 


440  STEAM-BOILER  ECONOMY. 

having  insufficient  heating  surface,  and  therefore  overdriven,  and  with 
unskilful  firing.  With  lignite,  or  lignitic  coal,  from  Utah,  a  figure 
as  low  as  3.79  Ibs.  has  been  obtained.  (Trans.  A.  S.  M.  E.,  vol.  iv. 
p.  263.)  The  writer  once  obtained  as  low  as  5.09  Ibs.  from  a  poor 
quality  of  Illinois  coal,  with  expert  firing,  with  the  boiler  driven  16 
per  cent  below  its  rating,  but  with  both  the  furnace  and  the  grate- 
bars  unsuited  to  the  coal.  (Trans.  A.  S.  M.  E.,  vol.  iv.  p.  267.) 

It  may  be  estimated-  that  with  any  kind  of  coal  the  evaporation 
per  pound  of  coal  will  be  in  the  neighborhood  of  15  per  cent  less  with 
a  rate  of  driving  of  6  Ibs.  of  water  from  and  at  212°  per  square  foot 
of  heating  surface  per  hour  than  at  a  rate  of  3  Ibs.,  the  rate  for  maxi- 
mum economy. 

Extent  of  Heating  Surface  Required. — For  factory  boilers,  or  for 
any  boilers  that  are  to  be  driven  at  a  uniform  rate  throughout  the 
day,  the  boilers  should  be  so  proportioned  that  the  rate  of  driving 
should  not  exceed  3  Ibs.  of  water  from  and  at  212°  per  square  foot  of 
heating  surface  per  hour ;  the  extra  cost  of  coal  for  driving  at  a  more 
rapid  rate  usually  being  greater  than  the  interest  on  the  extra  invest- 
ment necessary  to  secure  a  sufficient  extent  of  heating  surface  over 
and  above  that  required  for  more  rapid  rates  of  driving. 

With  boilers  for  electric  street-railway  service,  however,  the  case 
is  entirely  different.  The  heavy  load  upon  the  boiler-pJant  lasts  for 
only  about  two  hours  out  of  the  twenty-four,  and  unless  money  is  very 
cheap  and  coal  very  dear,  it  will  usually  pay  to  sacrifice  say  15  per 
cent  of  economy  during  those  two  hours  rather  than  go  to  the  expense 
necessary  to  proportion  the  boilers  so  that  they  will  be  driven  at  their 
most  economical  rate  during  those  two  hours.  It  is  also  to  be  con- 
sidered that  the  extra  boiler  which  is  to  be  put  in  the  plant  so  that 
any  one  boiler  may  at  any  time  be  laid  off  for  cleaning  or  repairs  may 
be  used  most  of  the  time,  since  repairs  and  cleaning  are  not  required 
often,  so  that  all  the  boilers  may  be  in  service  during  the  time  of  the 
peak  of  the  load  for  a  large  proportion  of  the  days  in  the  year,  and 
the  excessive  rate  of  driving  during  the  time  of  the  peak  of  the  load 
may  thus  be  diminished. 

It  will  therefore  not  be  bad  designing  if  the  extent  of  heating  sur- 
face is  proportioned  so  as  to  allow  of  the  boilers,  after  one  is  laid  off 
for  cleaning  or  repairs,  to  be  driven  at  a  rate  of  6  Ibs.  of  water 
evaporated  from  and  at  212°  per  square  foot  of  heating  surface  per 
hour  during  the  time  of  the  peak  of  the  load,  provided  that  no 
mistake  has  been  made  in  estimating  the  quantity  of  steam  needed 
during  that  time,  due  consideration  being  had  to  the  fact  that  the 
engines  are  wasteful  of  steam  when  overloaded,  as  they  are  likely  to 
be  during  that  time,  and  provided  also  that  sufficient  coal-burning 
capacity  is  provided  in  the  furnaces,  so  that  enough  coal  may  be 
burned,  including  the  15  per  cent  wasted  by  rapid  driving,  to  supply 
this  steam  under  the  most  unfavorable  conditions  of  wet  weather  and 
of  poor  coal. 

Assume  that  the  steam  engineer's  estimates  show  that  600  I.H.P. 


DESIGNING  BOILERS  FOR  STREET-RAILWAY  PLANT.      441 

will  be  required  to  be  furnished  by  the  engines  during  the  time  of 
maximum  load,  that  the  engines  are  non-condensing,  requiring  30  Ibs. 
of  steam  per  I.H.P.  per  hour  at  their  economical  load  and  20  per  cent 
more  when  overloaded  so  as  to  furnish  the  600  I.H.P.;  that  the 
feed-water  is  furnished  from  a  heater  at  200°  F.,  and  that  the  steam- 
pressure  is  125  Ibs.,  we  then  make  a  calculation  as  follows: 

600    I.H.P. 
30     Ibs.  steam  per  I.H.P.  per  hour. 

18,000     Ibs.  per  hour. 
Add 3,600     20  per  cent  for  overloaded  engines. 

21,600     Ibs.  per  hour. 
Mult.  by. . .   1.057     factor  of  evaporation  for  feed  at  200°  and  steam  of  125  Ibs. 

Product. ..  .22,831     Ibs.  equivalent  evaporation  from  and  at  212°  per  hour. 
Divide  by. .  6     Ibs.  evap.  per  sq.  ft.  heating  surface  per  hour. 

Quotient. . .   3,805     sq.  ft.  heating  surface. 

This  is  the  very  smallest  amount  of  heating  surface  that  should 
be  provided  for  the  given  conditions.  It  may  be  divided  among  two 
boilers  of.  not  less  than  1903  sq.  ft.  each,  or  three  boilers  of  1268 
sq.  ft.  each,  and  in  either  case  an  additional  boiler  of  the  same  size 
must  be  provided  so  that  one  boiler  may  be  laid  off.  The  plant  will 
therefore  contain  either  three  boilers  of  1903  sq.  ft.  each  =  5709 
sq.  ft.,  or  four  boilers  of  1268  sq.  ft.  each  —  5172  sq.  ft.  It  may  be 
found  that  the  three  larger  boilers  including  setting,  valves,  piping, 
etc.,  will  cost  little  if  any  more  than  the  four  smaller  boilers  with 
their  setting,  etc.,  and  it  may  also  be  considered  advisable  to  have  the 
three  larger  boilers,  with  their  greater  total  extent  of  heating  surface, 
to  provide  against  the  contingency  of  an  increased  amount  of  steam 
being  needed  by  the  engines. 

A  plant  of  three  boilers  is  a  favorite  arrangement  for  a  new  street- 
railway  plant,  two  of  the  boilers  being  set  in  one  battery  and  the  third 
singly,  a  space  being  left  alongside  of  the  third  boiler  for  a  fourth, 
completing  two  batteries,  if  ever  it  should  be  needed. 

Now  let  us  assume  that  the  coal  to  be  used  is  a  rather  low  grade 
of  Illinois  coal,  of  a  heating  value  of  14,300  heat-units  per  pound  of 
combustible,  and  that  it  may  be  expected  to  contain  occasionally  as 
high  as  18  per  cent  ash  and  12  per  cent  moisture.  The  heating  value 
per  pound  of  coal  will  then  be  14,300  x  .70  =  10,010  heat-units. 
This  divided  by  965.7  gives  10.36  Ibs.  of  water  from  and  at  212°  as 
the  possible  evaporation  of  the  coal  if  it  were  completely  burned  and 
all  the  heat  utilized  by  the  boiler.  But  only  a  portion  can  be  utilized, 
say  55  per  cent,  if  the  boiler  is  provided  only  with  an  ordinary  setting, 
or  say  65  per  cent  if  it  is  set  with  a  fire-brick  oven,  especially  designed 
to  burn  the  volatile  gases,  or  if  it  is  provided  with  a  down-draft  furnace 
or  a  mechanical  stoker  suitable  for  that  grade  of  coal.  The  difference 
in  economy  between  an  efficiency  of  55  per  cent  and  one  of  65  per 


442 


STEAM-BOILER  ECONOMY. 


cent  is  not  10  per  cent,  as  some  may  suppose,  but  10  -v-  65  =  15.4  per 
cent. 

We  now  make  the  following  calculation : 


Plain 
Furnace. 

Special 
Furnace. 

Heating  value  of  1  Ib.  of  coal,  equivalent  evaporation  from 
and  at  212°  

10.36 

10.36 

Efficiency  of  boiler  and  furnace  

.55 

.65 

Product  Ibs   from  and  at  212°         ..    .        

5.698 

6.734 

Deduct  15  per  cent  for  loss  due  to  driving  the  boiler  at  6  Ibs. 
per  sq.  ft.  of  heating  surface  per  hour,  or  double  its 
most  economical  rate  

855 

1.010 

Tjbs   water  evaporated  from  and  at  212°   per  Ib   coal         .... 

4  843 

5  724 

Divide  these  figures  into  the  figure  already  found  for  total 

22,831 

22,831 

4,714 

3,989 

The  difference,  725  Ibs.,  is  15.4  per  cent  of  4714  Ibs.,  which  agrees 
with  the  economy  of  the  more  efficient  furnace  as  above  stated  and 
checks  the  computation. 

Extent  of  Grate-surface  Required. — To  calculate  the  extent  of 
grate-surface  required  we  must  know  how  many  pounds  of  coal  may 
be  burned  per  square  foot  of  grate  per  hour.  This  will  depend  on  the 
draft,  on  the  kind  of  grate  used,  and  on  the  nature  of  the  coal  as  to 
free-burning  quality  and  as  to  its  clinker  ing  on  the  grates  and  choking 
the  air-supply.  We  may  assume  that  a  chimney  150  ft.  high  is  pro- 
vided, which  after  making  allowances  for  bends  in  the  flues  from  the 
boiler  to  the  chimney  will,  under  the  most  unfavorable  conditions  of 
weather,  give  a  draft  of  at  least  0.5  in.  of  water-column  at  the  end  of 
the  boiler.  The  coal  is  free-burning,  and  will  burn  rapidly  if  supplied 
with  enough  air  through  the  grate-bars,  but  it  clinkers  badly.  With 
ordinary  grates  we  cannot  count  on  burning  it  at  a  faster  rate  than 
25  Ibs.  per  sq.  ft.  of  grate  per  hour,  but  with  shaking  grates  well 
handled,  so  as  to  keep  the  fire  clear  of  clinker,  a  rate  of  35  Ibs.  may  be 
expected.  We  now  calculate  the  grate-surface  required  as  follows : 


Plain 
Furnace. 

Special 
Furnace. 

4,714 

3,989 

Plain  grates,  25  Ibs.  per  hour,  sq.  ft  

189 

160 

Shaking  grates    35  Ibs.  per  hour,  sq   f  t  .  .    .         

135 

114 

With  shaking  grates  and  hard,  steady  firing,  we  may  expect  a  loss 
through  the  grates  of  unburned  coal  amounting  to  about  2  per  cent 
more  than  the  loss  through  the  plain  grates,  but  as  in  a  street-railway 
plant  this  hard  firing  will  last  only  about  two  hours  a  day,  we  need 
make  no  change  in  our  calculation  on  this  account. 


DESIGNING  BOILERS  FOR  STREET-RAILWAY  PLANT.     443 


We  thus  have  four  different  figures  for  the  extent  of  grate-surface 
required,  according  to  whether  we  use  ordinary  or  special  furnaces 
and  ordinary  or  shaking  grates.  Dividing  the  heating  surface  already 
found,  3805,  by  these  figures,  we  have  for  the  ratio  of  heating  to  grate- 
surface  the  following: 


Plain  Furnace. 

Special  Furnace. 

Plain 
Grate. 

Shaking 
Grate. 

Plain 
Grate. 

Shaking 
Grate. 

•Sti    ft    of  grate                       .          ... 

189 
20.1 

135 

28.2 

160 

23.8 

114 
33.3 

Rcitio  heat'ins1  to  grate-surface 

These  figures  for  the  ratio  of  heating  to  grate-surface  are  very 
much  smaller  than  those  provided  in  the  common  designs  of  modern 
boilers,  especially  those  of  the  water-tube  type.  The  ratio  they  give 
usually  ranges  from  35  to  50.  The  reason  for  this  difference  is  that 
the  data  upon  which  the  above  calculations  are  based  are  very  different 
from  those  upon  which  these  boilers  are  designed.  We  have  assumed 
a  maximum  rate  of  driving  of  6  Ibs.  of  water  evaporated  from  and  at 
212°  per  square  foot  of  heating  surface  per  hour,  with  an  intentional 
sacrifice  of  economy  in  order  to  save  first  cost  of  installation.  We 
have  also  assumed  a  low  grade  of  coal  that  clinkers  on  the  grate,  and 
in  the  case  of  the  plain  furnace  a  low  efficiency.  In  the  design  of  the 
ordinary  water-tube  boiler,  especially  for  factory  purposes,  economy 
of  coal  is  the  first  consideration.  The  heating  surface  is  therefore 
made  of  such  an  extent  that  it  does  not  require  to  be  driven  at  a  rate 
greater  than  3  Ibs.  per  sq.  ft.  per  hour  on  an  average,  with  a  maximum 
of  4  or  4^  Ibs.  The  boilers  are  by  most  builders  rated  in  II. P.  at  the 
rate  of  3  Ibs.  evaporation  per  square  foot  of  heating  surface  per  hour, 
and  when  evaporation  tests  are  made  to  prove  guarantees  a  good 
•quality  of  coal  is  usually  obtained  and  the  boilers  are  driven  at  not 
above  4  Ibs.  per  sq.  ft.  of  heating  surface  per  hour. 

Another  reason  for  the  high  ratios  of  heating  to  grate-surface  in 
modern  water-tube  boilers  is  that  when  designed  with  a  view  to 
economy  of  first  cost  and  of  ground-space  occupied  they  are  made 
long,  narrow,  and  high,  so  as  to  pile  a  great  amount  of  heating  surface 
on  a  small  ground  area.  A  narrow  boiler  means  a  narrow  grate-sur- 
face, and  as  it  is  not  easy  for  a  fireman  to  handle  with  good  results  a 
grate  over  7  ft.  long,  it  means  limited  extent  of  grate-surface.  This 
is  all  right  for  good  semi-bituminous  coal  or  for  Pittsburg  or  Hocking 
Valley  bituminous,  which  are  both  free-burning  and  low  in  ash.  With 
these  coals  and  strong  draft  and  a  ratio  of  heating  to  grate-surface  of 
45  or  even  50  to  1,  it  is  possible  to  drive  the  boiler  to  double  its 
economical  rate.  For  poor  coals,  however,  whether  anthracite  or 
bituminous,  such  a  ratio  gives  entirely  too  small  a  grate  for  rapid 
driving. 


444  STEAM-BOILER  ECONOMY. 

About  three  years  ago,  in  a  series  of  tests  made  by  the  writer  on  a 
water-tube  boiler  with  a  very  poor  quality  of  Illinois  coal,  with  an 
ordinary  furnace  and  plain  grate-bars,  and  with  a  good  draft,  he  found 
that  only  about  85  per  cent  of  the  capacity  of  the  boiler  could  be 
developed  even  with  expert  firing.  The  chief  troubles  were  the 
clinkering  of  the  grates  and  the  excessive  amount  of  moisture  in  the 
coal,  which  retarded  the  combustion.  With  the  same  boiler  provided 
with  a  fire-brick  arch  setting,  with  shaking  grates,  and  with  Hocking 
Valley  lump  coal  the  boiler  was  driven  to  over  170  per  cent  of  its 
rating,  or  over  5.1  Ibs.  of  water  evaporated  from  and  at  212°  per  square 
foot  of  heating  surface  per  hour.  Had  it  been  possible  to  double  the 
extent  of  grate-surface  when  using  the  poor  grade  of  coal  it  is  quite 
likely  that  the  capacity  obtained  could  have  been  doubled. 

Having  made  the  calculation,  as  above  shown,  for  the  extent  of 
grate-surface  required  under  the  four  assumed  conditions,  we  must 
next  consider  which  one  of  the  four  results  should  be  adopted  in  the 
design.  Unless  coal  is  very  cheap  it  will  pay  to  go  to  any  reasonable 
expense  to  provide  the  special  furnace,  either  a  fire-brick  oven  built  in 
front  of  the  boiler  with  arrangements  for  burning  the  smoky  gases,  or 
a  down-draft  furnace,  or  a  mechanical  stoker.  With  any  of  these 
devices  a  saving  of  15  per  cent  in  fuel  should  be  expected  when  the 
coal  is  a  highly  volatile  bituminous.  Shaking  grates  are  also  desirable 
in  a  street-railway  plant  using  poor  fuel,  since  they  enable  the  grate  to 
be  kept  free  from  clinker,  and  diminish  greatly  the  grate-surface  and 
therefore  the  ground  area  required. 

Specifications  for  Bids. — Having  fixed  upon  the  extent  of  grate- 
surface  that  is  necessary  to  burn  the  coal  under  the  most  unfavorable 
conditions  of  weather,  moisture,  etc.,  for  the  heaviest  load,  adding,  of 
course,  the 'grate-surf  ace  for  the  extra  or  reserve  boiler,  this  should  be 
entered  in  the  specifications  for  bidders  for  boilers,  and  no  bid  should 
be  considered  which  did  not  give  the  full  extent  called  for.  Many 
expensive  mistakes  have  been  made  by  purchasers  of  boilers  who  have 
accepted  the  guarantees  of  economy  and  capacity  offered  by  builders, 
without  reference  to  the  extent  of  grate-surface.  After  erection  the 
boilers  may  be  proved  to  have  fulfilled  the  guarantees,  on  an  expert 
test,. with  good  coal,  but  afterwards  they  fail  to  develop  the  additional 
capacity  required  of  them  in  emergencies,  or  even  their  rated  capacity 
when  the  coal  is  poorer  than  that  used  in  the  test.  The  remedy  then 
usually  is  the  costly  one  of  obtaining  additional  boilers,  and  sometimes 
of  building  a  new  boiler-house.  The  purchaser  is  fortunate  if  he  can, 
by  a  change  in  the  style  of  furnace  or  of  grates,  or  by  building  a  taller 
chimney  or  by  introducing  forced  draft,  so  increase  the  capacity  of 
the  boilers  as  to  avoid  the  necessity  of  buying  additional  ones. 

The  extent  of  heating  surface  found  by  the  calculation  should  also 
be  entered  in  the  specifications  as  the  minimum  to  be  bidden  upon. 
Some  bidders  may  not  be  able  to  furnish  together  with  the  specified 
extent  of  grate-surface  as  small  an  extent  of  heating  surface  as  that 
called  for,  since  their  designs  are  not  adapted  for  such  small  ratios  of 


DESIGNING  BOILERS  FOR  STREET-RAILWAY  PLANT.      445 

heating  to  grate-surface  as  those  given  above,  but  there  is  no  objection 
to  their  furnishing  as  much  more  as  they  choose,  and  among  bidders 
offering  the  same  grate-surface  those  offering  the  greater  extent  of 
heating  surface  should  have  the  preference,  other  conditions  being 
equal.  Capacity  for  emergencies  being  obtained  by  extent  of  grate- 
surface,  economy  of  coal  will  be  obtained  by  extent  of  heating  surface 
above  that  needed  to  give  an  evaporation  at  the  rate  of  G  Ibs.  per  sq. 
ft.  of  heating  surface  per  hour. 

Bidders'  Guarantees. — Guarantees  of  economy  and  capacity  may 
be  inserted  in  specifications,  but  they  should  be  considered  secondary 
as  compared  with  dimensions  of  grate  and  heating  surface,  and  no 
attention  should  be  paid  to  guarantees  of  unusual  economy  offered  by 
any  bidder  who  does  not  give  any  more  heating  surface  than  other 
bidders,  unless  that  guarantee  is  based  upon  the  offer  of  a  special 
furnace  or  stoker,  which  may  reasonably  be  expected  to  give  better 
economy  than  a  plain  furnace  when  soft  coal  is  used. 

Type  of  Boiler. — The  calculations  made  as  above  described  are 
applicable'  to  any  type  of  boiler.  The  selection  of  a  type  depends 
on  other  considerations  than  capacity  or  economy,  for  these  depend 
upon  proportions  and  not  on  type.  These  considerations  are  safety, 
durability,  convenience,  or  facility  for  cleaning  and  making  repairs, 
ground  space  occupied,  ability  to  furnish  dry  steam  when  overdriven,, 
and  last  of  all,  cost. 

Loss  of  Fuel  Due  to  Keeping  Up  Steam-pressure  in  Idle  Boilers.— 
In  a  report  J>y  F.  K.  Low  to  the  Committee  on  Data  of  the  National 
Electric  Light  Association  (Electrical  World,  June  12,  1897)  some 
statistics  were  presented  showing  the  amount  of  coal  required  to  keep 
up  pressure  while  no  steam  or  water  is  being  taken  from  the  boiler. 
We  quote  from  the  report  as  follows : 

When  a  boiler  is  laid  off  it  becomes  a  drag,  the  coal  used  in 
maintaining  the  fire  in  a  condition  to  be  started  counting  for  nothing, 
so  far  as  steam-production  is  concerned.  The  engineer  of  a  Phila- 
delphia station  on  a  test  found  that  it  required  1200  Ibs.  of  buckwheat 
coal  to  keep  up  a  pressure  of  125  Ibs.  on  two  water-tube  boilers,  having 
each  59  sq.  ft.  of  grate-surface.  This  was  0.424  Ibs.  per  sq.  ft.  of  grate- 
surface  per  hour. 

A  five-days'  test  of  a  horizontal  tubular  boiler  showed  a  consump- 
tion of  .35  Ib.  of  coal  per  sq.  ft.  of  grate.  Another  water-tube  boiler 
in  a  five-days'  test  used  0.5  Ib.  per  sq.  ft.  of  grate. 

A  Lancashire  boiler  with  mechanical  stokers  used  only  0.2  Ib.  of 
coal  per  sq.  ft.  of  grate  on  a  seven-days'  test. 

Two  other  water-tube  boilers,  one  on  a  seven-days'  test  and  the 
other  on  a  test  of  several  days'  duration,  used,  respectively,  0.7  and 
0.5  Ib.  of  coal  per  sq.  ft.  of  grate. 

In  each  of  these  cases  the  boiler  was  shut  off  from  the  main  and 
no  steam  or  water  taken  from  it.  The  coal  was  used  simply  to  main- 
tain the  pressure.  A  moderate  rate  of  combustion  is  12  Ibs.  per  sq.  ft. 
of  grate  per  hour.  Allowing  0.5  as  the  average  consumption  while 


446 


STEAM-BOILER  ECONOMY. 


standing,  the  coal  burned  by  a  boiler  in  this  way  would  be  4.17  per 
cent  of  that  burned  while  running  at  12  Ibs.  per  sq.  ft.  of  grate  for  the 
same  length  of  time. 

If  a  boiler  runs  sixteen  hours  a  day  at  an  average  rate  of  12  Ibs. 
of  coal  per  sq.  ft.  of  grate  per  hour,  and  stands  the  other  eight  with  a 
consumption  of  0.5  Ib.  per  sq.  ft.  of  grate  per  hour,  the  coal  used,, 
while  idle,  will  be  2.04  per  cent  of  the  whole.  If  it  runs  half  the  time, 
the  expense  in  coal,  while  standing,  will  be  4.17  per  cent  of  the  total 
amount.  The  following  table  gives  the  percentages  for  different 
lengths  of  running  and  different  rates  of  combustion : 


Percentage  of  Total  Coal  Used  in  Idle  Boilers  at  .5  of  a  Pound  per 
Square  Foot  of  Grate  While  Idle. 

Hours 
Running. 

Hours 
Standing. 

Average  Rate  Combustion  per  Square  Foot  Grate  While  Running. 

12 

15 

18 

20 

24 

23 

1 

.18 

.15 

.12 

.11 

.10 

22 

2 

.38 

.30 

.25 

.23 

.19 

21 

3 

.59 

.47 

.40 

.36 

.28 

20 

4 

.83 

.66 

.55 

.50 

.41 

19 

5 

1.08 

.87 

.66 

.65 

.55 

18 

6 

1.37 

1.10 

.92 

.83 

.69 

17 

7 

1.69 

1.35 

1.13 

1.02 

.85 

16 

8 

2.04 

1.63 

1.37 

1.23 

1.03 

15 

9 

2.44 

1.92 

1.64 

1.48 

1.23 

14 

10 

2.89 

2.33 

1.99 

1.75 

1.44 

13 

11 

3.40 

2.73 

2.30 

2.07 

1.70 

12 

12 

4.00 

3.23 

2.70 

2.44 

2.04 

11 

13 

469 

3.79 

3.18 

2.87 

;  2.40 

10 

14 

5.51 

4.46 

3.75 

3.38 

2.83 

9 

15 

6.50 

5.26 

4.42 

400 

3.35 

8 

16 

7.69 

6.25 

5.26 

4.76 

3.85 

7 

17 

9.19 

7.41 

5.96 

5.79 

4.87 

6 

18 

11.11 

9.09 

7.69 

6.98 

5.88 

Coal  Used  in  Banked  Fires  not  a  Measure  of  Loss  by  Radiation,— 

The  heating  value  of  the  coal,  used  when  the  boiler  is  idle,  averaging, 
according  to  Mr.  Low's  report,  4.17  per  cent  of  that  used  when  it  is 
in  operation  and  burning  12  Ibs.  of  coal  per  sq.  ft.  per  hour,  is  not  to 
be  considered  a  correct  measure  of  the  heat  lost  by  radiation,  since 
when  the  fire  is  banked  or  the  draft  nearly  all  shut  off,  the  coal  con- 
sumed is  burned  with  an  insufficient  supply  of  air,  and  therefore 
develops  less  than  its  full  heating  value.  The  gases  evolved  from  the 
smouldering  fire,  whether  burned  or  unburned,  escape  into  the 
chimney  at  about  the  temperature  of  the  steam  in  the  boiler.  The 
coal  burned  while  the  boiler  is  idle  therefore  represents  the  sum  of 
three  different  heat  losses,  viz.,  that  due  to  imperfect  combustion,  the 
heat  carried  into  the  chimney,  and  the  heat  lost  by  radiation. 


ECONOMY  IN  ELECTRIC-LIGHT  STATIONS. 


447 


Assuming  a  ratio  of  heating  to  grate-surface  of  40  to  1,  a  rate  of 
driving  of  3  Ibs.  of  water  per  square  foot  of  heating  surface  per  hour 
and  an  evaporation  of  8  Ibs.  of  water  per  pound  of  coal,  gives  a  rate 
of  combustion  of  15  Ibs.  of  coal  per  square  foot  of  grate  per  hour,  a 
fair  figure  for  water-tube  boilers  with  anthracite  coal.  Taking  the 
consumption  per  hour  with  banked  fires  as  0.5  Ib.  per  square  foot  of 
grate,  gives  3^  per  cent  of  the  hourly  coal  consumption  when  running, 
a  figure  which  covers  all  the  losses  of  heat  due  to  banking  fires.  The 
loss  due  to  radiation  should  be  considerably  less  than  this  figure. 

Steam-boiler  Economy  in  Electric-light  Stations.* — The  difference 
between  the  performance  of  boilers  reported  for  long  periods  under 
widely  varying  capacities,  and  charged  with  all  the  coal  used  for 
banking,  etc.,  and  their  normal  efficiency  under  test  conditions,  is 
shown  in  the  following  table,  where  the  "  test  duty  "  is  the  best  result 
obtainable  under  the  best  conditions  with  the  fuel  used ;  the  "  actual 
duty  "  is  the  number  of  pounds  of  water  evaporated  in  a  long  term  of 
service,  divided  by  the  coal  used  in  the  same  period.  The  third 
column  is  the  ratio  of  the  actual  to  the  test  efficiency,  showing  how 
badly  the  efficiency  was  impaired  by  the  conditions  of  actual  service. 

With  the  exception  of  No.  11,  the  apparently  low  efficiency  of 
which  was  due  to  a  low  grade  of  Western  coal,  these  results  are  sur- 
prisingly high : 


No. 

Test  Duty. 

Actual  Duty. 

Ratio  Actual 
to  Test. 

1 

2 

3 

4 

8.58 
8.68 
9.96 

8.009 

7.302 

8.02 
7  5 

94.5 

84.1 
80.5 

5 
6 

10.5 

9.96 
10  00 

94.6 
95  24 

7 
8 

7 

6.14 
6  04 

87.71 

9 
10 
11 

11.2 
10.8 

9.83 
9.85 
5  75 

87.71 
97.72 

12 

11  36 

13 

7  50 

14 

9  00 

Where  the  grate-surface  is  ample,  a  very  cheap  grade  of  fuel  can 
be  used  with  a  considerable  reduction  of  the  cost,  and  it  is  suggested 
that  an  economical  advantage  may  arise  from  using  two  grades  of  fuel 
in  plants  that  run  long  hours  with  widely  varying  loads;  a  good 
steaming  coal  with  which  the  boilers  can  be  forced  at  the  time  of  over- 
load, and  a  cheap  small  coal  which  can  be  used  to  advantage  on  the 
otherwise  spare  grate-surface  when  the  load  is  below  the  average. 

*  From  a  Report  by  F.  R.  Low  to  the  Committee  on  Data  of  the  National  Elec- 
tric-light Association.     (Electrical  World,  June  12,  1897.) 


448 


STEAM-BOILER  ECONOMY. 


Cost  of  Coal  per  Boiler  Horse-power  per  Year. — Taking  a  com- 
mercial or  boiler  horse-power  as  an  evaporation  equivalent  to  34£ 
Ibs.  of  water  from  and  at  212°  per  hour,  the  evaporation  per  pound 
of  coal  under  actual  conditions  of  feed-water  temperature  and  steam- 
pressure  at  from  5  to  10  Ibs.,  and  the  cost  of  coal  per  ton  of  2240  Ibs. 
at  from  $1  to  $5,  we  obtain  the  following  figures  for  cost  of  coal  per 
horse-power  per  year  of  3600  hours,  or  12  hours  per  day  for  300 
days  in  the  year,  and  per  year  of  8760  hours,  or  24  hours  per  day 
for  365  days. 

COST   OF   COAL   PER   BOILER   HORSE-POWER   PER  YEAR. 


Water 
Evap. 
per  Ib. 
of 
Coal. 

Coal 
per 
Boiler 
H.P. 
per  hr. 

Year  of  8600  Hours.. 
Cost  of  Coal  per  Ton. 

Year  of  8760  hours. 
Cost  of  Coal  per  Ton. 

Ibs.] 
10 
9 
8 
7 
6 
5 

Ibs. 
3.45 
3.83 
4.31 
4.93 
575 
6.90 

11. 

5.94 
6.16 
6.93 
7.92 
9.24 
11.09 

$2. 

11.09 
12.32 
13.86 
15.84 
1848 
22.18 

S3. 

16.63 
18.48 
20.79 
28.76 
27.72 
33.27 

2-3.18 
24.64 
27.72 
31.68 
36.96 
44.36 

$5. 

27.72 
30.80 
34.65 
39.60 
46.21 
55.45 

11. 

13.49 
14.99 
16.86 
19.27 
22.49 
26.98 

$2. 

26.98 
29.98 
33.73 
38.55 
44.97 
53.97 

$3. 
40.48 
44.97 
50.59 
57.82 
67.46 
80.95 

$4. 

53.97 
£9.96 
67.46 
77.10 
89.95 
107.94 

$5. 

67.46 
7496 
84.32 
96.37 
112.43 
134.92 

Boiler-room  Labor. — An  investigation  made  in  1896  for  the  Steam- 
users'  Association  of  Boston,  Mass.,  by  Mr.  K.  S.  Hale,  led  to  the 
following  conclusions  concerning  the  cost  of  boiler-room  labor : 

In  plants  containing  595  boilers  the  coal  consumption  was  8302 
tons  per  week,  or  700  tons  per  boiler  per  year  of  50  weeks.  The 
average  cost  of  boiler-room  labor  per  ton  of  coal  handled  was  48  cents, 
ranging  from  26  to  74  cents. 

The  cost  gradually  decreases  as  the  size  of  the  plant  increases, 
becoming,  however,  nearly  stationary  at  200  tons  per  week. 

The  men  fire  more  coal  (in  the  proportion  of  about  15  per  cent) 
and  receive  more  pay  (about  10  per  cent)  in  the  plants  that  run 
twenty-four  hours  a  day  instead  of  ten  hours  a  day,  the  result  being 
a  cost  per  ton  about  5  pier  cent  less.  The  difference  is  not  quite  so 
marked  when  comparing  plants  burning  very  large  amounts  of  coal 
(200  tons  a  week). 

The  labor  per  ton  of  coal  is  about  10  per  cent  less  for  a  steady 
load  than  for  a  variable  load  of  any  sort. 

Handling  coal  should  cost  about  1.6  cents  per  ton  per  yard  up  to 
five  yards,  then  about  0.1  cent  per  ton  for  each  additional  yard. 

Cheap  men  do  as  much  work  as  good  men,  so  that  the  cost  of 
labor  is  almost  always  less  per  ton  of  coal  with  cheap  men.  The 
quality  of  the  work  may  not  be  the  same,  so  that  the  cost  per  ton  of 
steam  is  not  necessarily  less. 

Wages  of  firemen  and  work  done  per  man  are  about  the  same 
from  Maine  to  Pennsylvania.  • 


STEAM-BOILER  PRACTICE  OF  THE  FUTURE,  449 

One  man  (besides  night  man)  can  run  engine  and  fire  up  to  about 
10  tons  per  week. 

One  man  (besides  engineer  and  night  man)  can  fire  up  to  about 
35  tons  per  week. 

Two  men  (besides  engineer  and  night  man)  can  fire  up  to  about 
55  tons  per  week. 

Three  men  (besides  engineer  and  night  man)  can  fire  up  to  about 
80  tons  per  week. 

These  figures  assume  that  the  night  man  does  all  he  can  of  the 
banking,  cleaning,  and  starting. 

The  figures  are  for  average  conditions.  If  the  conditions  are 
exceptional,  as,  for  instance,  a  very  long  wheel  or  very  variable  load, 
proper  allowance  should  be  made. 

Mechanical  stokers  save  30  to  40  per  cent  of  labor  in  very  large 
plants  (over  200  tons  per  week),  20  to  30  per  cent  in  medium-sized 
plants  (50  to  150  tons  per  week),  and  save  no  labor  in  small  plants. 

Handling  Coal  and  Ashes  in  Large  Plants. — Mr.  Ilale's  report 
gives  no  data  of  the  cost  of  handling  coal  in  large  modern  plants,  such 
as  electric -light  and  power-stations.  In  the  best  modern  practice  the 
coal  received  by  car  or  boat  is  elevated  and  dumped  in  large  storage- 
bins  under  the  roof  of  the  boiler-house  by  means  of  suitable  hoisting 
and  conveying  machinery.  "Vrom  the  bins  it  is  led  down  by  means  of 
iron  pipes  and  fed  by  gravity  directly  into  the  hoppers  of  the  mechan- 
ical stokers.  The  ashes  are  dumped  from  the  ash-pits  of  the  several 
boilers  into  cars  or  storage-bins  in  a  tunnel  underneath.  By  such 
mechanical  methods  of  handling  both  coal  and  ashes  all  shovelling  is 
avoided,  and  the  cost  of  boiler-room  labor  per  ton  of  coal  may  thus  be 
made  much  less  than  the  lowest  figure  named  in  Mr.  Ilale's  report. 

Steam-boiler  Practice  of  the  Future. — Steam-boiler  practice  at  the 
present  day  is  in  a  rather  chaotic  state.  There  is  a  confusing  multi- 
plicity of  types  and  of  varieties  of  each  type.  With  any  given  style 
of  boiler  and  furnace  there  is  a  lack  of  uniformity  in  the  capacity  and 
economy  obtained  from  boilers  of  the  same  size  in  different  places. 
It  is  not  uncommon  to  find  two  or  three  different  styles  of  boilers  in 
the  same  boiler-house.  In  a  row  of  four  or  five  boilers  of  the  same 
size  and  style,  the  arrangement  of  the  flues  may  differ,  so  that  no  two 
of  them  have  the  same  draft,  and  consequently  no  two  of  them  develop 
the  same  power  or  give  the  same  economy. 

Besides  the  variety  in  types  and  in  the  conditions  of  running  of 
existing  boilers,  there  is  a  tendency  to  change  in  the  conditions.  The 
pressure  of  steam  required  by  engines  is  increasing.  The  small  sizes 
of  anthracite  are  being  used  instead  of  the  larger  sizes,  and  they 
require  stronger  draft,  and  larger  grate-surfaces,  and  give  more  trouble 


4:50  STEAM-BOILER  ECONOMY. 

to  handle  ashes  and  clinker.  Soft  coal  is  in  many  places  displacing 
anthracite,  bringing  with  it  smoky  chimneys,  and  as  the  smoke  nuis- 
ance increases  new  devices  are  continually  being  brought  forth  to 
suppress  it.  Real  estate  in  cities  is  becoming  more  costly,  and  boilers 
are,  therefore,  designed  to  economize  space,  and  they  are  being  driven 
at  more  rapid  rates.  Rapid  driving  with  bad  water  means  more 
trouble  from  scale,  and  this  enlarges  the  business  of  makers  of  feed- 
water  purifiers,  scale-extracting  machinery,  and  "  boiler  compounds." 
This  is  the  age  of  labor-saving,  and  in  order  to  reduce  the  labor  cost 
of  steam-making  automatic  stokers  and  mechanical  means  of  handling 
coal  and  ashes  are  introduced. 

The  changes  above  mentioned  are  now  in  progress,  but  the  day 
when  stationary  steam-boiler  practice  shall  reach  a  reasonable  degree 
of  uniformity,  such  as  has  been  reached  in  locomotives  and  in  marine 
engines  and  boilers,  seems  yet  far -distant.  The  fittest  will  survive  at 
list,  but  the  unfit  lives  a  long  time. 

The  following  is  a  list  of  the  leading  types  and  varieties  of  boilers 
which  still  survive  in  stationary  practice  in  the  United  States : 

Internally  Fired. — Galloway,  Scotch  marine,  locomotive,  vertical 
tubular. 

Externally  Fired. — Shell  boilers:  cylinder,  two-flue,  horizontal, 
and  vertical  tubular ;  water-tube  boilers :  inclined,  vertical,  and  curved 
tubes;  coil  or  pipe  boilers. 

Besides  these  there  are  numerous  combined  and  nondescript  types, 
and  modifications  of  standard  types,  which  usually  have  but  a  short 
life  in  the  market. 

There  is  no  probability  that  any  increased  economy  of  fuel  may 
be  obtained  by  a  change  from  any  one  type  to  another,  if  the  condi- 
tions of  driving  remain  the  same.  With  any  one  of  these  types  an 
efficiency  of  from  70  to  nearly  80  per  cent  of  the  theoretically  possible 
may  be  obtained  from  good  anthracite  or  semi-bituminous  coal,  low  in 
ash  and  moisture,  and  burned  thoroughly  in  a  properly  designed 
furnace,  the  boiler  being  driven  at  its  most  economical  rate,  and 
proper  provision  being  taken  to  lessen  the  losses  from  radiation  and 
from  leaks  of  air  through  tne  boiler-setting. 

The  Survival  of  a  Type  will  Depend  on  Some  Other  Factor  than 
Economy  of  Fuel. — The  possible  economy  that  may  be  obtained  from 
all  types  being  equal,  the  standard  type  or  types  of  the  future  will  be 
selected  for  other  reasons  than  economy  of  fuel.  Chief  among  these 
reasons  are :  (1)  Safety  from  explosion.  (2)  First  cost.  (3)  Durability. 


STEAM-BOILER  PRACTICE   OF  THE  FUTURE. 


451 


(4)  Facility  for  cleaning.  (5)  Cost  of  repairs  and  facility  for  making 
them.  (G)  Space  occupied.  (7)  Possibility  of  driving  at  both  low  and 
high  rates  of  evaporation  without  great  loss  of  fuel  economy.  (8) 
Adaptability  of  the  boiler  and  furnace  to  different  kinds  of  coal,  so 
that  the  coal  may  be  changed  as  market-prices  vary. 

The  seventh  reason  in  this  list  may  require  some  explanation.  It 
is  found  in  testing  boilers  at  different  rates  of  driving  that  the  fuel- 
economy  bears  some  relation  to  the  rate  of  driving,  but  that  the  law 
of  this  relation  varies  with  the  type  of  boiler,  and  even  in  the  same 
boiler  when  fired  with  different  coal  or  under  different  circumstances. 
In  Fig.  134  the  upper  line  A  shows  the  maximum  economy  obtained 


1 

1 

2 

._. 

g  '* 

A 

^ 

"* 

*.- 

-- 

-- 

^ 

"~* 

«-^ 

2 

/ 

Tt 

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-^ 



-i^ 

V- 

'•». 

^ 

3 

/ 

/' 

^N 

"^^ 

-x. 

^ 

V" 

-  ^ 

f\    <JL 

/ 

xs 

""- 

^ 

"*• 

% 

C/ 

^ 

\ 

X 

^ 

s^. 

s 

\ 

\ 

^ 

H 

\ 
\ 

5 

/; 

7 

\ 
\ 

F 

r'° 

** 

--. 

i 

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§ 

""  - 

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a 

ft  * 

6 

§ 

to 

JLBS.OF  WATER  PER  SQ.FT.OEAXIXG  SURFACE  FES  HOUR. 

Fro.  134. — RELATION  OF  ECONOMY  TO  RATE  OF  DRIVING. 

A,  maximum  results  at  the  Centennial  Exhibition;  1,  Firmenich;  2,  Root;  3, 
Smith;  4,  Galloway;  B  and  C,  two  hypothetical  cases;  D,  minimum  results  at 
the  Centennial  Exhibition;  E}  5,  7,  Exeter;  F,  6,  8,  Wiegand. 

at  different  rates  of  driving  in  tests  of  four  boilers  at  the  Centennial 
Exhibition,  viz. :  The  economy  of  tests  of  the  Firmenich  and  Root, 
and  the  capacity  tests  of  the  Smith  and  Galloway  boilers.  It  is  con- 
ceivable that  there  might  have  been  a  single  boiler  which  would  have 
given  these  four  results,  which  would  have  been  an  extraordinary,  but 
not  impossible  record.  The  line  D  joins  the  lowest  results  obtained 
in  the  Centennial  tests  at  the  rates  of  driving  shown.  The  results  of 
the  other  tests,  if  plotted,  would  fall  inside  of  the  area  bounded  by  the 
lines  A  and  D.  The  relation  of  rate  of  driving  to  economy  of  the 
Exeter  boiler  is  shown  by  the  line  E,  and  that  of  the  Wiegand  boiler 
]}y  the  line  F.  The  lines  B  and  C  represent  the  hypothetical  cases  of 


452  STEAM-BOILER  ECONOMY. 

two  boilers  tested  at  a  number  of  different  rates.  While  boiler  O 
shows  the  highest  economy,  it  is  only  for  a  limited  range  of  the  rate 
of  driving  that  its  economy  is  greater  than  that  of  B,  the  latter  showing 
a  higher  economy  over  a  wide  range,  and  therefore  it  may  be  con- 
sidered the  better  boiler,  as  far  as  economy  of  fuel  is  concerned,  for 
widely  varying  loads,  while  C  is  the  better  for  steady  driving  at  a  rate 
which  corresponds  to  that  of  its  maximum  economy. 

The  Boiler  Types  of  the  Future. — There  is  not  likely  to  be  any 
important  change  in  the  existing  types  of  boiler  used  in  stationary 
practice,  nor  is  any  new  type  likely  to  be  developed  which  will  offer 
any  advantages  over  the  present  types.  New  boilers  or  modifications 
of  old  ones  will  continue  to  be  invented,  and  some  of  them,  by  dint  of 
business  enterprise  and  liberal  advertising,  may  be  sold  in  considerable 
numbers,  but  the  farther  these  depart  in  their  construction  from  the 
existing  types  the  less  likely  are  they  to  be  permanently  successful. 

The  survival  of  certain  types  in  the  struggle  between  those  now  on 
the  market  will  depend  not  on  economy  of  fuel,  as  has  already  been 
stated,  nor  on  cheapness  of  first  cost,  for  as  the  country  increases  in 
wealth,  boiler  users  become  more  willing  to  pay  fair  prices  for  the  best 
boilers.  It  will  depend  chiefly  on  the  factors  of  durability  and  facility 
for  cleaning  and  for  repairs.  Durability  depends  largely  on  the  kind 
of  water  used  in  a  boiler,  and  therefore  a  boiler  may  survive  in  New 
England,  where  the  water  is  generally  of  excellent  quality,  while  it 
may  be  condemned  in  many  sections  of  the  West,  where  the  water 
contains  large  amounts  of  scale-forming  material.  The  question  of 
economy  of  space  occupied  will  be  an  important  factor  in  determining 
the  type  of  boiler  to  be  used  in  large  plants  in  cities,  where  real  estate 
is  expensive. 

Boiler  Furnaces  of  the  Future. — The  greatest  improvement  which 
is  to  be  made  in  average  boiler  practice  is  the  adoption  of  furnaces  for 
burning  soft  coal  without  smoke.  In  ordinary  practice  in  the  Western 
States  an  efficiency  of  50  per  cent  or  less  is  not  uncommon,  with  the 
coal  burned  in  ordinary  furnaces.  It  is  quite  possible  to  raise  this  to 
70  or  even  75  per  cent  with  automatic  stokers,  furnaces  surrounded 
by  fire-brick,  and  provision  for  securing  the  intimate  admixture  of  very 
hot  air  with  the  distilled  gases.  The  raising  of  the  efficiency  of  boilers 
by  these  means  from  50  per  cent  to  70  per  cent  would  effect  a  saving 
of  many  millions  of  dollars  per  year,  and  it  would  at  the  same  time 
abolish  the  smoke  nuisance,  which  is  an  increasing  one  in  all  large 
cities. 


INDEX. 


Acme  stoker,  174 

Air,  heated,  use  <3f  in  furnaces,  163 
properties  of,  18 
required  for  combustion,  19 
supply,  calculation  from  analysis  of 

gases,  32 

supply,  effect  of  varying-,  331 
supply,  excess  formula  for,  34 
supply,  experiments  in  varying,  381 
Alabama  coal-field,  67 
Alaska  coal-fields,  83 
Allen  water-tube  boiler,  260 
Almy  water-tube  boiler,  2G4 
Alternate  method  of  firing,  161 

of  starting  and  stopping  a  test,  337, 

369 

American  underfeed  stoker,  177 
Analyses  of  coal,  proximate,  352 
of  different  coals,  see  Coal. 
of  gases,  340,  397 
of  gases  may  be  erroneous,  437 
Analysis,  proximate,  relation  to  heating 

value,  103,  108 

Anderson  water-tube  boiler,  404 
Andrews  boiler,  403 
Anthracite,  burning  small  sizes,  148 
in  Pennsylvania,  53 
early  use  of,  54        . 
results  obtained  from,  289 
Appalachian  coal-field,  56 
Apparatus     for     determining     heating 

value  of  coals,  128 

for  indicating  furnace  conditions,  434 
Argaud  steam-blower,  154 
Arizona  coals.  80 
Arkansas  coals  76 
Arndt's  econometer,  435 
Ash,  character  of,  44 

Bnbcock  &  Wilcox  stoker,  172 
water-tube  boiler,  266,  276,  393 

Bagasse  as  fuel,  137 
burner,  Cook's,  187 

Banking  fires,  loss  due  to,  445 

Belleville  water-tube  boiler,  263 

Bidders'  guarantees,  445 


Bids,  specifications  for,  444 
Blechynden's  experiments  on  transmis- 
sion of  heat,  235 

Block  coal,  Ohio  and  Indiana,  68,  69 
Blowers,  steam-  and  fan-,  tests  of,  150 

the  Argand,  154 
Boiler,  Andrews,  403 
Cornish,  248 
double  cylinder,  247 

elephant*  248 

Exeter  cast-iron,  404 

Galloway,  248 

Harrison  cast-iron,  404 

Lancashire,  248 

locomotive,  255 

Lowe  tubular,  403 

Manning  vertical,  253 

Pierce  rotating,  405 

plain  cylinder,  188,  200 

plain  cylinder,  disadvantages  of,  200 

practice  of  the  future,  449 

return  tubular,  250 

Scotch  marine,  255 

Smith  tubular,  403 

two-flue,  248 

types,  evolution  of,  247 

vertical  tubular,  251 

Webber  vertical,  252 
Boiler,  water-tube,  Allen,  260 

Almy,  264 

Anderson,  404 

Babcock  &  Wilcox,  266,  276 

Belleville,  263 

Cahall,  271 

Cal dwell,  267 

Church,  261 

Dance,  262 

Field,  259 

Firmenich.  265 

Fitch  &  Voight,  258 

Fletcher,  259 

Gill,  267 

Gurney,  261 

Hazelton,  261 

Joly,  259 

Kelly,  260 

453 


454 


1NDEX. 


Boiler,  water-tube,  Kilgore,  263 

Maynard,  265 

Miller,  259 

Morrin's  Climax,  274 

Mosher,  276 

National,  267 

Phleger,  262 

Roberts,  264 

Rogers  &  Black,  262 

Root,  267 

Rowan,  262 

Stevens,  258 

Stirling,  272 

Thornycroft,  275 
,   Ward,  263 

Wheeler,  265 

Wickes,  272 
(  Wiegand,  260 

Wilcox,  261 

Boiler-compounds,  319,  322 
Boilers,   forms  used  in  different  coun- 
tries, 277      '; 

Bomb  calorimeter,  Mahler's,  94 
British  Thermal  Unit,  3 
Briquettes,  or  pressed  fuel,  131 
Brown  coal  and  lignite,  43 
Buckwheat  anthracite  coal,   tests  with, 

386 
Bunte,  tests  of  German  coals,  116 

Cahall  water-tube  boiler,  271 
Caldwell  water-tube  boiler,  267 
California  coal,  81 
Calorimeter,  coal-,  Mahler's,  94 

steam-,  338,  353 

correction  for,  354 
Calorimetric  tests  of  coals,  87,  126 
Cannel  coal,  43 
Capacity,  depends  on  economy,  192 

elementary  principles,  188 

of  a  boiler,  10 

of  a  plain  cylinder  boiler,  188,  200 
Carbon,  16 

monoxide  due  to  heavy  firing,  31 

monoxide  formed  from  CO2,  12 
Centennial  Exhibition  tests,  290,  402 
Chain-grate  stokers,  172 
Chemistry  of  fuel  und  combustion,  16 

of  scale  and  scale-solvents,  323 
Chimney-draft  theory,  422 
Chimney  height  for  different  fuels,  426 

table  of  sixes  of,  428 
Church  water  tube  boiler,  261 
Circulation  of  water  in  boiler,  299 

effect  of,  on  economy,  240 
Classification  of  coals,  42 

Griiner's,  87 

Climax  water-tube  boiler^  274 
Coal,  analyses  of,  in  various  districts, 
46,  54  to  83,  85,  87,  93,  104,  112, 
114,  117 


Coal,  analyses  and  heating  value,  45 

and  f-ocial  progress,  38 

anthracite,  in  New  Mexico,  56 

anthracite,  in  Pennsylvania,  53 

brown,  and  lignite,  43 

caking  and  non-caking.  43 

calorimetric  tests,  87,  93 

cannel,  43 

classification  of,  42,  87 

effect  of  weathering,  116 

formation  of,  39 

graphitic,  in  Rhode  Island,  52 

heating  value  of,  44 

hygrometric  properties  of,  36 

moisture  in,  41     . 

production  of,  in  U.  S.,  39,  40 

quality  of,  in  relation  to  boiler  capa- 
city, 50 

sampling  of,  339 

selection  of,  for  steam-boilers,  119 

semi-anthracite,  54 

soft,  how  to  burn,  155 

testing  relative  values  of,  121 

valuing  by  test  and  analysis,  51 
Coal-dust  as  fuel,  132,  183 

burning,  Wegener  system,  183 

De  Camp  system,  182 
Coal-fields  of  the  United  States,  52 

bituminous  and  semi-bituminous, -56 
Coals,  tests  of  heating  value  by  Bunter 
116 

Hale  &  Williams,  113 

Johnson,  84 

Lord  &  Haas,  101 

Mahler,  92 

Scheurer-Kestner,  84 

Slosson  &  Colburn,  112 
Code  of  rules  for  boiler-trials,  333 
Coefficient  of  performance,  "a,"  220 
Coke,  131 

Coking  system  of  firing,  159 
Colorado  coals,  78 
Combustible,  definition  of,  12 
Combustion,  chemistry  of,  16 

heat  produced  by,  20 

heat  of,  7 

of  fuel,  8 

imperfect,  8 

rate  of,  due  to  height  of  chimney,  425 

complete,  how  to  secure,  159 
Commercial   and  experimental  results, 

361 

Complaints  concerning  boilers,  301 
Connellsville  coal,  46 
Corn  as  fuel,  144 
Cornish  boiler,  248 
Corrosion,  internal,  313 

external,  328 
Cost  of  coal  per  boiler  horse-power,  448 

of  labor  in  boiler-rooms,  448 

of  handling  coal  and  ashes,  449 


INDEX. 


455 


Coxe  automatic  stoker,  170 
Culin,  anthracite,  tests  with,  386 
Cumberland,  Md.,  coal,  46 
coal-field,  62 

Dance  water-tube  boiler,  262 
DeCamp  powdered-coal  system,  182 
Decomposition,  heat  absorbed  by,  21 
Defects  causing  explosions,  3*29 

discovered  by  inspection,  329 
Definitions  and  principles,  1 
Designing  boilers  for  a  railway  plant, 

437 
Distribution   of    the    heating   value    of 

•    fuel,  360 

Down-draft  furnace,  165 
Draft,  due  to  height  of  chimney,  424 

forced,  179 

force  or  intensity  of,  423 

gauge,  362 

induced,  180 

poor,  302 
Dulong's  formula  for  heating  value,  7, 

93,  103 

Durability,  296,  328 
Durston's  experiments  on  transmission 

of  heat,  239 
Dust-fuel,  132,  183 

Econometer,  Arndt's,  435 

Economizers,  430 

saving  effected  by,  432 

Economy,  calculation  of,  191 
depends  on  rate  of  driving,  196 
elementary  principles  of,  188 
of  boilers  in  electric  stations,  447 
of  fuel  does  not  depend  on  type,  293 
range  of  found  in  practice,  380 

Efficiency,  calculation  of,  341 

does  not  depend  upon  type  of  boiler, 

242 

effect  of  various  conditions  on,  221 
general  formula  for,  219 
of  a  boiler,  11 
of  boiler  and  grate,  359 
of  the  heating  surface,  14,  205 

Electric-light  stations,  boilers  in,  447 

Elephant  boiler,  248 

ElJJs  &  Eaves  hot-air  system,  182 

Equivalent  evaporation,  11 

Evaporation,  factors  of,  416 
tests,  332 

Exeter  cast-iron  boiler,  404 

Experiments,  see  Tests. 

Explosion,  danger  of,  295 

Explosions   caused   by  hidden   defects, 
329 

Factors  of  evaporation,  416 
Feed-water,  quality  of,  313 
Field  water-tube  boiler,  259 


Firing,  improper,  307 

mechanical,  166 

methods,  with  anthracite,  147 

with  soft  coal,  155 
Firmenich  water-tube  boiler,  265 
Fitch  &  Voight's  water-tube  boiler   258 
Flame,  9 

Fletcher  water-tube  boiler,  259 
Flue-gas  analysis,  366 
Forced  draft,  179 
Fuel  and  combustion,  16 
Fuels  other  than  coal,  131 

mixed,  heating  value  of,  21 
Furnace  not  adapted  to  coal,  304 
Furnaces  for  anthracite  coal,  147 

for  bituminous  coal,  155 

for  burning  tan-bark,  136,  187 

Hawley  down-draft,  165 

Kent's  wing-wall,  161 

location  of,  145 

requirements  of,  146 

usa  of  heated  air  in,  163 

Walker,  160 
Future  boiler  and  furnace  practice,  449 

Galloway  boiler,  248 

Gas  analyses  and  the  heat  balance,  436 

Gases,  weight  and  densities  of,  20 

weight  of,  calculated,  32 
Gas-fuel,  142 
Georgia  coals,  67 
German  coals,  Bunte's  tests,  116 
Gill  water-tube  boiler,  267 
Graphic  record  of  a  test,  372 
Graphitic  coal,  in  Rhode  Island,  52 
Grate  and  heating  surface  required  for 
given  power,  282,  285 

bars,  air-space  through, ^288 

bars,  151 

the  McClave,  153 
Grates,  shaking  and  dumping,  153 
Grate-surface,  calculations  of,  440 

large  ratios  of,  443 

insufficient,  304 
Grooving  or  channelling,  317 
Guarantees  in  bids,  445 
Gurney  water-tube  boiler,  261 

Harrison  cast-iron  boiler,  404 
Hawley  down-draft  furnace,  165 
Hazelton  water-tube  boiler,  261 
Heat,  2 

absorbed  by  decomposition,  21 

balance.  341,  360,  436 

latent,  4 

of  combustion,  7 

quantity  of,  6 

specific,  4 

transfer  of,  10 

transmission  through  plates,  235,  239 

unit,  definition  of,  3 


456 


INDEX. 


Heated  air,  use  of  in  furnace,  163,  181, 
Heating  surface,  calculations  of,  440 

efficiency  of,  205 

insufficient,  195,  311 

•measurement  of,  284 

required  for  given  power,  283 
Heating  value  of  coals,  84,  128 

available,  of  hydrogen,  22 

of  hydrogenous  fuels,  24 

relation  to  fixed  carbon,  108,  110 
Heating  values  of  pure  fuels,  20 

of  compound  fuels,  21 

of  various  substances,  20 
Horse-power  of  a  steam-boiler,  11,  280 

builder's  rating,  285 
Hot-air  system,  Howden,  181 

Ellis  &  Eaves,  182 
Howden's  hot-air  system,  181 
Humidity,  relative,  18 
Hydrogen,  16 

available  heating  value  of,  22 
Hygrometric  properties  of  coals,  36 

Illinois  coal-basin,  69 

coals,  70 
Indiana  coals,  69 
Incrustation  and  scale,  317 
Indian  Territory  coals,  77 
Inspection,  facility  for,  298 
Iowa  coals,  74 

Johnson's  tests  of  American  coals,  84 
Joly  water-tube  boiler,  259 
Jones  under-feed  stoker,  179 

Kelly  water-tube  boiler,  260 
Kent's  wing- wall  furnace,  161 
Kentucky,  eastern,  coal-field,  65 

western,  coal-field,  69 
Kilgore  water-tube  boiler,  263 

Lancashire  boiler,  248 
Latent  heat,  4 

of  steam,  408 

Leakage  of  air  through  brickwork,  306 
Life  of  a  steam-boiler,  328 
Lignite,  43 
Liquid  fuel,  see  Petroleum,  137 

advantages  of,  141 
Lord  and  Haas's  tests  of  American  coals, 

101 

Loss  of  fuel  due  to  banking  fires,  445 
Lowe  horizontal  tubular  boiler,  403 

Mahler's  coal  calorimeter,  94 
tests  of  European  coals,  92 
Manning  vertical  boiler,  253 
Marine  boilers,  255,  275,  276 
Maryland  semi-bituminous  coal,  46,  62 
Maynard  water-tube  boiler,  265 


Measures  for  comparing  duty,  282 
Megass,  see  Bagasse,  137 
Michigan  or  northern  coal-field,  G8 
Miller  water-tube  boiler,  259 
Missouri  coal-basin,  74 
Moisture  in  coal,  method  of  finding,  339, 
351 

in  steam,  353 

in  steam,  determination  of,  374 
Montana  coals,  81 
Morrin  water-tube  boiler,  274 
Mosher  boiler,  276 
Murphy  automatic  furnace,  176 

National  water-tube  boiler,  267 

Nevada  coal,  81 

New  Mexico,  anthracite  in,  56 

coals  of,  80 

New  River,  W.  Va.,  coal,  46 
Nitrogen,  17 
North  Carolina  coal,  64 
North  Dakota  coal,  81 

Ohio  coals,  67,  105  , 

Oil,  methods  of  burning,  184 
Oil,  petroleum  as  fuel,  137 

versus  coal,  141 
Operation  of  a  steam-boiler,  12 
Oregon  coals,  82 

Orsat  apparatus  for  analyzing  gases,  366 
Oxygen,  17 

required  for  combustion,  19 

Peat  or  turf,  133 
Pennsylvania  anthracite,  46,  54 

bituminous  coals,  46,  59 
Performance  of  boilers,  289 
Petroleum  as  fuel,  137 

methods  of  burning,  184 
Phleger  water-tube  boiler,  262 
Pierce  rotating  boiler,  405 
Pittsburg  coal,  46,  104 
Play  for  I  stoker,  172 
Pocahontas  coal-field,  63 

coal,  104 

Points  of  a  good  boiler,  292 
Powdered  fuel,  132,  183 
Practical     conclusions     derived     from 

theory,  228 

Precautions  in  boiler-testing,  349 
Pressed  fuel,  or  briquettes,  131 
Principles  and  definitions,  1 
Producer-gas,  143 

Proportions  of  grate  and  heating  sur- 
face, 282 

of  flues  and  gas-passages,  288 
Pyrometers,  435 

Quality  of  steam,  corrections  for,  355 

superheated  steam,  358 
Quantity  of  heat  in  a  body,  6 


INDEX. 


457 


Radiation,  effect  of,  on  efficiency,  210 

method  of  measuring,  373 

loss  due  to,  446 

Railway  plant,  designing  boilers  for,  437 
Rating  of  boilers,  11 
Repairs  of  boilers,  297 
Report  of  a  boiler-trial,  forms  for,  342 
Retarders,  181 

Rhode  Island,  graphitic  coal  in,  52 
Ringelmann's  smoke-chart,  364 
Roberts  water-tube  boiler,  264 
Rogers  &  Black  water-tube  boiler,  262 
Roney  mechanical  stoker,  173 
Root  water-tube  boiler,  267 
Rowan  water-tube  boiler,  262 
Rules  for  conducting  boiler-trials,  333 

Sampling  flue-gases,  365 
Sampling  of  coal,  339 
Sawdust  as  fuel,  135 
Scale  and  incrustation,  317 

causes  of,  321 
Scheurer-Kestner's    tests   of   European 

coals,  84 

Scotch  marine  boiler,  255 
Selection  of  coal  for  steam-boilers,  11& 
Selecting  a  new  type  of  boiler,  292 
Semi-bituminous  coal-fields,  56 

coal,  analyses,  46,  59 
Setting  of  boiler,  bad,  305 
Smith  boiler,  403 
Smoke,  how  it  may  be  burned,  8 

how  to  avoid,  156 

measurements,  364 

observations,  341 

preventing  furnace,  requirements  of, 
158 

prevention,  success  of,  157 
Smoke-chart,  Ringelmann's,  364 
Smoky  chimneys  not  necessary,  156 
Specifications  for  bidders,  444 
Specific  heat,  4 

heat  of  ilue-gases,  228 
Spence's  experiments  in  varying  the  air- 
supply,  381 

Standard  method  of  starting  a  test,  336 
Starting  and  stopping  a  test,  336,  369 
Steam-  and  fan-blowers,  tests  with,  150 

calorimeter,  use  of,  338 

dry,  identification  of,  410 

dryness  of,  299 

jets  for  preventing  smoke,  164 

properties  of,  408 

quality  of,  correction  for  ,  355 

table,  410 

use  of  under-grates,  148 
Stevens  water-tube  boiler,  258 
Stirling  water-tube  boiler,  272 
Stokers,  mechanical  or  automatic,  166 

Acme,  174 

American,  177 


Stokers,  Babcock  &  Wilcox,  172 

Coxe,  170 

Jones  under-feed,  179 

Murphy,  177 

PI  ay ford    172 

Roney,  173 

Vicars,  169 

Wilkinson,  176 
Straw  as  fuel,  136 
Sulphur,  17 

heating  value  of,  35 

heating  value  of,  in  coal,  35 
Superheated  steam,  quality  of,  358 
Superheating,  how  determined,  338 

Tan-bark  as  fuel,  136 
Temperature,  2 

due  to  burning  carbon,  26 

"     "        "        hydrogen,  24  and  27 
of  the  firer  25 
theoretical,  26 
Tennessee  coals,  66 
Test,  graphic  record  of  a,  372 
Testing  relative  value  of  coals,  121 
Tests,  computation  of  results,  376 
evaporation,  object  of,  332,  348 
of  a  Babcock  &  Wilcox  marine  boiler, 

393 

of  a  Thornycroft  boiler,  398 
of   Stirling    boilers    with    anthracite 

coal,  386 
of    two-  flue   boilers  with   Pittsburg 

coal,  392 
rules  for.  333 

with  anthracite  at  the  Centennial  Ex- 
hibition, 290,  402 
with  small   sizes  of  anthracite  coal, 

383 

Texas  coals,  78 
Thornycroft  marine  water-tube  boiler, 

275,  398 

Transfer  of  heat,  10 
Transmission    of   heat  through  plates, 

235,  239 

Trials,  see  Tests. 
Troubles  and  complaints,  301 
Turf  or  peat,  133 

Under-feed  stokers,  177,  179 
Unit  of  evaporation,  4 
Urquhart  oil-burner,  187 
Utah  coals,  80 

Valuing  coals  by  test  and  by  analysis, 

51 

Vicars  automatic  stoker,  169 
Virginia  anthracite,  55 
coal-fields,  63 

Ward  coil-pipe  boiler,  263 
Washington  coal,  82 


-.458 


INDEX. 


Waste  beat,  method  of  saving,  202 
Water,  properties  of,  406 

and  steam-capacity,  298 

level,  steadiness  of,  299 
Water,  quality  of  feed-,  813 
Water-tube  boilers,  258 

using  waste  gases  of  a  plain  cylinder 

boiler,  202 

Weathering  of  coal,  116 
Webber  vertical  boiler,  251 
We«ener  powdered-coal  system,  183 
West  Virginia  coals,  64,  104 
Wet  tan-bark,  furnaces  for,  136,  187 


Wheeler  water-tube  boiler,  265 
Wickes  water-tube  boiler,  272 
Wiegand  water-tube  boiler,  260 
Wilcox  water- tube  boiler,  261 
Wilkinson  stoker,  176 
Wood,  analysis  of,  41 

as  fuel,  134 

heating  value  of,  135 
Wyoming  coal,  80 

Youghiogheny  coal,  46 

Zinc,  use  of  to  prevent  corrosion,  316 


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6 


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ENGINEERING. 

CIVIL — MECHANICAL— SANITARY,  ETC. 
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GINEERI.NG,  p.    11  J    MECHANICS   AND    MACHINERY,  p.  12  ;  STEAM 

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7 


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8 


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10 


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11 


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Wood's  Co-ordinate  Geometry 8vo,  2  00 

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12 


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13 


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14 


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15 


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Woodhull's  Military  Hygiene , '. .  .16mo,       1  50 

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16 


OF  THE 

UNIVERSITY 


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